Leader LBO-520 Oscilloscope repair help

[YoshiKnuuckles]

Well, I'm back at it again trying to fix this old scope. I have the service and owners manuals, and I've read over the Tektronix scope troubleshooting guide. I believe something is wrong with the vertical amplifier or vertical pre-amplifier.

I've dragged it in to my school's lab to work on it (they have the equipment I need to do so,) and I'm about to leave for the day so I won't be able to do anything else till tomorrow.

What I've done so far:

-Tested the voltage rails, they all appear to be OK.
-Started the calibration procedure, which went well until I reached the step titled "MATCHING adjustment of Delay Line." I was able to get it calibrated, and gained a clue to this scope's fault, which I took a video of.

https://youtu.be/ClHPE3mwp4Q

The waveform looks ok other than the amplitude being ~0.5 CM off when at the top half of the display(I'm guessing the vertical gain is off? That's the next step in calibration,) but as it is moved to the bottom it distorts and collapses in on itself. I'm feeding in a ~100Khz square wave at about 80mVp-p from an HP 3312A Function Generator, and have the proper waveform displayed on one of the school's scopes. Both probes are set to a 1x attenuation ratio.

I know the scope still needs a lot of calibration, but I'd like to figure out what is causing the fault before I continue, as I'll likely have to recalibrate it all over again afterwards. Any ideas or suggestions on what to check when I get here tomorrow would be wonderful.

[oldway]

This is clearly a failure.
Never attempt to calibrate a faulty scope: it must be repaired before any calibration attempt.
This failure does exist on one or on both channels?

[YoshiKnuuckles]

The failure exists on both channels. The scope appears to be functioning properly other than the fault I've shown. I'm admittedly a beginner, hence why I didn't realize to find the fault first! I was simply following the service manual.

[YoshiKnuuckles]

Looked it over when I got to the college this morning, and found that the Vertical Final amplifier is missing transistor Q315, which looks like it was desoldered from the board!   

Taking a look at the schematic for the scope, it shows that it is supposed to be there, and is a 2SC1012A transistor. Hmm. This might explain a lot.

Datasheets for 2SC1012A: http://www.datasheetarchive.com/2SC1012A-datasheet.html

Having a bit of trouble finding an equivalent part. This one looks to be the closest I could find that is available: http://www.digikey.com/product-detail/en/2SC2258/2SC2258-ND/279299

I found that part through one of the equivalent transistor datasheets. Wondering if I'd be ok with that one.