Helping a buddy with his 17 axys rmk 800. Last year it had an occasional bog and on our last ride dropped a cylinder. He also mentioned the idle slowly decreased throughout the winter. Under the assumption the motor was toast he tore it down and let it sit all summer. The pto piston on the intake side on the corner of the skirt was worn/scratched a little and nikasil was slightly chipped. Nothing that would’ve made me guess it wouldn’t run on that cylinder. So disappointed with what I saw I figured this would be a headache as i knew the motor wasn’t the problem. He sent out the injectors has them tested and cleaned as I thought it could be a possibility. They were fine. So I helped get the motor buttoned up with new Polaris pistons and replated cylinders from millennium (not the same set, he exchanged his junk ones for newly replated ones) and let him do the rest of the assembly. With fresh plugs new relays and fresh gas fired it up. It now runs on both cylinders but not the best. Only idles 1500 rpm and hiccups a lot - it likes to pop and almost backfire throughout different rpm kinda acting like a fouled plug which it’s not. So back apart it came. Inspected the reeds those look fine. Then I look at the piston. It’s wearing already in the SAME spot with 1 mile on the new pistons. I attached. Pic. So I’m guessing air leak from a leaking crank seal. Other than that my only other guesses are TPS or fuel pump related but the pump doesn’t whine. Any thoughts? I know it’s a long read but I REALLY appreciate any new ideas. Thank you.