OK, the first thing I did was shotgun all the 'lytic caps in the power board, that made a difference in the sound quality that was somewhat expected, clearing this up a bit, please note, my 5050 was in really nice shape having been in a studio that, along with 3 others, did ADC. So this one had been used very little, and changing the caps I expected would help a bit, and it did, and was a good idea if for no other reason than to provide a bit of insurance for longevity...
however, where things really improved was a suggestion, quite strongly given, that the metallized film caps in the 18V rails that feed the audio sections, be replaced with film and foil caps. I'm in the camp that wonders about the changes caps make to gear, not sure I buy all that PIO, film/foil, etc., etc., stuff. Well, my mind has been changed! The difference was immediate and is improving over time, and was not subtle to my hearing, deeper soundstage, clearer instruments, you could really hear those violin strings against the bows, much fuller sounds. Tapes that were really good took on a vividness that was amazing, some tapes that were marginal, like the Phase 4 recordings, sounded so much better, and some that were OK were not so hot. There are 14 of these caps in the rails and I used some 192P caps that fit pretty well in the smallish spaces. Would be interested in hearing from someone else that does this upgrade to confirm, I still cannot believe the difference it made. There were other suggestions that I will get to as well...