For me it depends on which RC and where on the RC. I have been learning over the years for ex.. that letting LST2 clutch bearings go til they "go" is a bad idea.. Better to just replace with new every gallon to gallon and a half.. Because it sucks to be out somewhere and have them go out.. First time it happened I thought my engine was toast, or the 2-speed, etc.. Nope, clutch bearings shot. This has happened a couple times.

I never really change other bearings - especially wheel bearings. Diff bearings OK if while I'm rebuilding they look or feel gritty or something..