Nanofrog, I use a 10 ml syringe with a 21 ga needle cut flat. With just a little practice I am able to drop a tiny bead on a pad and spread it with the tip of the needle. I probably do use a bit more than using a fine paintbrush or a refillable pen, but the syringes and needles are free. My wife works at a Dr. office and brings them as I need them. I might try the paint brush, what size do you use? I would think at least a 4-0. If you decide to get one of those pens, let us know what you think.
Don't have access to free syringes (must be nice
), and I'm not sure of a good source that's inexpensive. Does seem like you'll have a lot of control though.
Not sure on the size (bench is completely cleared for the shelving project & stuffed in boxes or wherever I could find a hole), but based on a chart I found, it's probably a #2 round (2/32"). Waste isn't bad due to size. Chisel type, would probably be another story if it's a small job or taken in spells, which is more of how I tend to do things (rely on the solder wire most of the time).
They do require cleaning though, so it's as convenient as a disposable pen or the refillable model mentioned. I really like the brush idea better than the hard felt or plastic nibs, and when I saw refillable, that got my attention.
Found a source on eBay for one ($5.99), and the box it's photographed with looks genuine. But I'm not sure due to the cost, as they're $15+ everywhere else I've looked. Might use it as a filler item from All-Spec. If I do go ahead and get one, I'll let you know.
I usually only use a needle bottle for tinning wire & drag soldering, so not that big a deal.
I found a seller on eBay that sells small quantities of Kester 186 if you're interested (sells 951 too). The 186 seems to be genuine to me (behaves well, and smells as I remember). Can't justify buying it by the gallon (would need to sell of the majority of it), so I gave the seller a chance (~$6 IIRC for the size I got). Previously, I'd use MG Chemicals liquid rosin, as they sell a 125ml bottle. The Kester is a bit lower in solids (36% vs. 50%, so it's a bit easier to clean IMHO). Not as active though IIRC, so YMMV, depending on if you're repairing stuff that's heavily oxidized or building on boards that are relatively new.