I have the piston, wrist pin, clips, gaskets and cylinder removed from my 2010 S50 last year. The engine had just over 300 miles at the time I replaced it with the Malossi 49mm piston and cylinder. I have listed it several times on fEeBaY for $0.99 without success. If you have a 4-valve 50 that needs a refresh, send a PM if you're interested. Pay the $13xx for the Medium Flat Rate box and it's yours. I hate to throw good stuff out.
You can see it Here.