The Maxima Castor927 did gum up my rings and powervalves. As far as when to slap a top end in, I follow the compression tester for that.
Service limits are:
upper: 165psi
lower: 110psi
Mine has a couple wide open desert races ( over a hundred miles at a shot), and alot of trail and play riding and it is hold 140 psi. If I had to guess I would say I have well over 100 hours on this topend. Ever since I started following the service limits and using my compression tester I spend ALOT less money on topends.