But that's not specifically what I'm looking for in this post.
OK, but what does "affordable" mean in that post?
The Tektronix TAS 485 is maybe the most repairable old 'scope but a decent one will cost you as much as a brand new DSO.
I'm not looking for all bells and whistles, something with your standard controls would suffice for my purposes.
Basic stuff like number of channels and bandwidth would be good to know as well...
Yeah no luck, and I didn't have the money at the time for another scope.
So now I'm looking for something better documented, so I don't have to go hunting for a blurry, tangentially related manual for something with no history.
Any recommendations?
Once I was in exactly your shoes and quickly learnt that despite the great old manuals available there was only so far you could go fixing a scope without another one. 
Schematics with DC voltages listed really help but only so far as things like sweep linearity can only be checked with another scope......as you discovered.
So after investing in my first DSO many more scopes were able to be taken on for repair however the reliability of older scopes was always a problem however many owners of them probably didn't have the sad run I saw with many but you have to decide if you wanna have to repair your scope before you can tackle a project which only adds to blood pressure and frustration in your pursuits in the fabulous industry.
Your budget is quite sufficient to get you a quite reasonable DSO which will give many years of trouble free service.
Dip your toes in the water and come on in, the water's fine. 
I can relate to the sentiments of the original poster, but time has really moved on in scopes...
In the 80's through to early 2000's I used a variety of reasonable spec analogue scopes for repair/project/ham radio uses - the usual suspects like Philips, (PM3262) Tectronics, (can't remember the model numbers of those) dual channel delayed timebase 100Mhz etc etc, for their day they were decent and worked fine, certainly for repair/troubleshooting work on mostly analogue circuitry.
Then in 2009 I packed my bags and moved across the world and the bench Tectronics scope I still had at that time had to be let go as it was too bulky and expensive to ship overseas in relation to its low value by that time... the only scope I kept, which surely must be a curiousity item / museum piece now, (and a feat of miniaturisation in 1979) was a battery powered Non Linear Systems MS-215:
http://www.byan-roper.org/steve/manuals/NLS/Non-linear_Systems_MS215_Miniscope_Manual.pdfDespite now being 42 years old (and over 20 years old when I first came into possession of it) it still works fine, aside from the sealed gel cell batteries which have failed for a 2nd time in the 20 years I've had it due to lack of use letting the cells discharge and sit discharged.
So someone wanting an old analogue scope to "play around with" which has a schematic which is easily understood and repaired might have fun with one of these - it even has a full circuit diagram in the owners manual!
For the last 10 years I haven't had much need for a scope so I've made do with the MS-215 for the occasional mostly audio work on my own equipment, but obviously there is only so much you can do with a 2" screen.
Recently I needed to repair some audio equipment and realising the gel cells in the MS-215 had failed again and I couldn't be bothered trying to source replacements I decided it was finally time after about 15 years to treat myself to a half decent new scope (and try to get back into electronics more as a hobby) and had a look to see what was available.
That's when it really hit me how much scopes have moved on in the last 20 years and that analogue scopes are basically dead and buried during my absence.
Of course there were digital scopes 20 or more years ago but not in the price range of your average repair technician, (you looked at them in glossy magazines but didn't own one...) they had significant limitations for analogue signals, and were more useful for their storage / single shot capture abilities but weren't ideal for analogue work especially high RF.
That has all changed. I started out looking at the ubiquitious Rigol DS1054Z as a friend has one, then I found out about the Siglent SDS1104X-U which is basically the same price but arguably a better device, then finally I stretched myself to the SDS1104X-E on the basis that it had additional features that could be unlocked over time that the SDS1104X-U didn't have, as well as better sampling with multiple channels and a few additional features.
So while it was undoubtedly massive overkill for the specific use I had in mind that pushed me to buy a new scope, I was thinking ahead for other things I could use it for and I have already used it for several other applications with great success.
Even though it's still only a low to mid "entry level" scope I'm in love with it and it blows me away what it can do compared to the scopes I've owned in the past that have all been analogue. Even simple stuff like single shot capture and hold or roll mode for very slow signals (which can't be shown on standard persistence analogue scopes) are features that I would have killed for 20 years ago. There are so many features packed into this device it's an unbelievable bargain.
Of course lower end digital scopes do still have some minor drawbacks - the 8 bit A/D resolution can bite you if you're not aware of it - particuarly apparent in X-Y mode, and you need to learn and understand the relationships of sample rate, memory depth etc, to get the best out of it vs an analogue scope where you're really only thinking about timebase and risetime performance of the scope/probe. So there is a learning curve, but it didn't take me long.
This scope will do everything that any scope I've owned before will, do it better and do 10x as many other things on top of that. In some ways I wish I'd made the jump a few years ago, on the other hand I didn't really have a need until more recently and the last 5 years seems to have been a particularly good time for entry level DSO's where the prices have come down dramatically and performance has gone up dramatically to the point where it becomes a no-brainer.
To the original poster - by all means find a cheap analogue scope as something to play around with - I won't be getting rid of my MS-215 any time soon, and one day I will replace its faulty gel cells to get it working again as I still think it's a kinda cool relic of the past due to its tiny size and portability, but for actual work and getting things done a modern DSO - even a good entry level one like the SDS1104X-E is simply amazing compared to any analogue scope you will have used and you won't be disapointed. It's a completely different world.
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