Quoted from craif:

I've got about 600 plays on my machine and the flippers have been getting weaker and weaker since about 300.
At first I thought it was just coil fade from extended play sessions, but then it started becoming noticable even in the first game or two of the day and my laser thermometer said they were barely above 90.
Cleaned and releveled around 400. Checked the stops and they seemed fine, but I had spares on hand so I replaced them anyway. The sleeves had some typical black dust but most of it just fell off and they look way better than the ones I've replaced in other machines in the past with no visible signs of damage or deformation. Didn't have spares on hand for those so they went back in until I get a shipment in. Mechs & shaft were pristine.
Seemed marginally better after that, but still bad. Took a serious dive in the last 50 to where even the first game it's difficult to clear the center ramp even from a full cradle on the right flipper and once any fade sets in even the left flipper can barely do it.
Have more sleeves on the way, but assuming that's not it any other ideas?

Quoted from craif:

I forgot to check that but they seem to have the right amount of play. However, after moving them up and down I played a game and thought they felt a little stronger than before. Still weaker than before all this started, but it makes me wonder if the there's some gunk in the bushing or on the shafts binding them up just a bit that got broken when I pulled them up and down to test the play. I'm not sure I'll get around to pulling them apart tonight, but it's something else to look at at least.
Years ago I knew a mechanic who would wax flipper shafts as part of his maintenance routine but I can't remember anyone mentioning it in the last decade. Is that still a thing? Was it ever?