06 250r, oil on spark plug threads, 62 hours, new piston?

The last piston went in at 35 hours.

I bought the bike with 40 hours on it and the right intake valve zero'd(got a killer deal!).

shimmed the right, but the left intake, and both exhaust valves were good.

now at 62 hours, having trouble starting, left intake valve now at zero. right intake(no movement after initial adjustment and 20 hours of riding) and exhaust valves good.

I pulled the plug, while not oil fouled, found oil on the threads. Also had oil on the threads when I pulled the plug just before my last ride.

is it time for a rebuild or can I just shim the left intake and keep riding it?

obviously if money weren't an issue, I would be doing the top end!

50/50 trail and mx riding. though I don't really scream it off the rev limiter.

I would just do rings and a hone and shim valves.

Until valves are on the move I wouldn't touch them. That seems to be what others on this site have recomended as well.

Ill post pics of the piston.

looks to be in good shape, no excessive scratching on the skirt, and the coating is still present

one valve has been replaced before and the other one shimmed.

but the replacement valve is moving again!

How about the valve cover leaking around the plug and running down.

Then you pull the plug it covers the threaded area.

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