Time to replace that engine. I would bet my paycheck that the sleeve is damaged also. OS is very proud of their engines, and the price of spares reflects that thinking.
The only other cost effective option would be to get a crashed OS .50 cheap and strip the parts needed to get this engine running again.
I did this to get a MOKI 1.35 running again after it ingested a wrist pin retaining clip and sustained severe piston/sleeve damage. I bought up a crashed MOKI 1.35 for $40 and combined the good parts I had to get a excellent engine. I got lucky. The price of new parts would have been around $200, give or take a few.................

Post a ad in the RCU engine wanted section and wait. Maybe you'll get lucky.

Mike