The no reverse symptom sounds like something I ran into a couple of months ago:
My parent's have a '90 Legacy 4-sp auto with exactly 80,000 miles on it. They've owned it since new. My dad was mentioning to me that it reverse was acting up. Shift it into reverse and it would just sit there and go nowhere for a long while.... worse when cold. I asked dad how long ago the Tranny Fluid/Filter had been changed.... and the answer was "NEVER"! 80k on original fluid! I was shocked, to say the least.
Next day I drained and dropped the pan. The fluid was a nasty brown color. Got about 2 more quarts out when I dropped the filter. 6.5 quarts refilled it, so I only got a bit more than 50% out, but what a difference! Shifts nice and reverse is no problem now.
I'll drain/refill again in a few months to get more of the old stuff out.
Short version: from my limited experience a new filter and fluid may fix the problem. Dont' pass up the '92.
