Got it all back together with the TBT kit (plastics not spring kit) and it feels good. Tried it with JSB exact 8.4 grain, and Exact 7.87 grain. The heavier pellet subjectively feels nicer, but the express has a slight edge in accuracy. Mind you the rifle is still running in, so probably too early to make a judgement. Any other pellets you've tried that worked well for you?
Incidentally, I did have the start of a galling issue after about 50 pellets. Stripped it again and modified the cocking arm according to threads I've studied on here. There were rough edges on the cocking shoe and the knuckle joint was all but seized. Fixed all those issues as well as removing the spring under the delrin bar.Now it feels smoother than when I first shot it out of the box. Fingers crossed.....