Oh ya, one more thing.

When I used to drive really old cars instead of just moderately old cars, I had pretty good luck with using Rislone to free up stuck lifters. It's a simple concentrated solvent, doesn't cost much, and you can pick it up at autozone.

Run that for 1k miles in combination with some relatively thin oil, and then change the oil and filter and do it again. It eats out the varnish, and will probably solve your problem, if it really is a stuck lifter.

Some people swear by the idea of dumping a quart or two of ATF in the crankcase, since apparently it's got a lot more detergents in it than motor oil and even most motor oil additives, but I could never screw up the courage to try that myself.