Not sure if this is a lvl 10 issue or not, so if this actually IS, my apologies.
Used RT classic, lvl 10, was leaking down the bolt. Bought new spacers, went down a half size (2.5 to 2, if I remember correctly) and the leak stopped.
Now, I find that the bolt doesn't seem to fully reset all the time. I might get 5-10 shots off and the next shot is a dry-fire. I physically push the ball into the breech (doesn't take much effort, ball plops right in) and it'll usually fire. Sometimes it'll vent (like it should with a ball that's not all the way seated), but next shot always fires.
I pulled the 2 out and put the 2.5 back in and we're back to the leak again. Didn't check to see if the ball hang was still there or not.
I've tried three different brands/quality of paint, and it doesn't matter.
I'd purchased and used a rebuild kit for the Classic (not lvl 10 rebuild kit).