whunter,
flushing with acetone is a good idea. I'm well familiar with this stuff, from my previous life, and it has earned my respect -- it's a great solvent (and also forms explosive mixture with air easier than many other organic solvents). As for the compressor: the advice that I've seen most often is to fill the compressor with new oil, rotate X times by hand, dump oil out, repeat. That's what I did. Replacing all seals would be obviously much harder, since I lack the proper tools for a compressor overhaul. What is the risk of running a compressor with some residual amount of old oil left absorbed in the seal? (I don't know if PAG oil was ever in there) If the only risk is the future compressor failure, wouldn't it be worth taking that risk instead of replacing the compressor up front? Since I'm doing my own work, I don't see the benefit of replacing the compressor proactively. I know that a catastrophic compressor failure may send 'black death' dust into the system, but I'm willing to flush it out and install an inline filter if that happens. Since the amount of oil absorbed in the seal is miniscule, I think it would be OK to ignore the moisture that may be present in that oil (and minute amounts of moisture are only a real concern if R12 is used, as I understand, and I hope that any old leftover oil will be long washed out and pumped through the receiver-dryer before I switch to R12). Are there any other risks that I'm not aware of?

Larry,
I did plan on flushing the evaporator initially, but my condenser flushing experience made me doubtful. Plus, I'd have to remove that new expansion valve I just installed... but that's not really a concern. I just feel uneasy about not knowing whether I got all of the liquid out of that evaporator or not. I'm trying to weight the risk of that vs. the risk of having a bit of old (mystery) oil left in the system. Evaporator already got washed with all that UV dye (a few oz) that was circulating in the system for about 5 min...

bonehead,
I got a Mastercool flush gun -- a cylinder with a hose on the bottom and a flush attachment on the end of the hose. Shop air is added on top of the cylinder.

Phil,
The reason 8 applications of UV dye went into the system was me looking for leaks... I did pill vacuum on it first thing, and the system was losing about .5" Hg per hour. UV dye went in, and a couple oz of R-134a. Turned out that the expansion valve was leaking, on the right side (looking from inside the car). I replaced the valve, and at that point the system would hold 29" vacuum for more than a day. There could still be a very slow leak someplace, can't tell with the gauges I got. Thus the plan to put in R-134a and see whether it still leaks. I read all/most of the great R12 vs R-134a threads, and ended up deciding to give R-134a a shot, with the expectation that it'll suck (I'm in Austin, the car is black, and the car is 24 years old, so the evaporator is likely half-blocked on the outside). I got my 609 certification, and am prepared to shell out $30 per can for R12 when the time comes, it's abundantly available on eBay (local auto shops sell it too, but ask closer to $50 a can). I don't like R12 on environmental grounds (I disagree with most people on the forum regarding 'junk science'), but in my case the case for R12 is likely to be too strong, and I'm not an environmental zealot to ignore common sense.

Old Deis,
I do use an air compressor. I know dry nitrogen is the proper way of doing it, but I ain't got any, nor do I have the facilities to store it. I'm counting on the air compressor not to blow much oil into the system. I didn't see any residue after flushing out a few hoses and the condensor, so I don't think external residue is an issue.

Thanks everyone for the advice, I really appreciate it.