I came across a nice looking 520 on ebay with bar and chain. I was hoping I could simply do a carb rebuild, but I discovered it has a very scored piston. Any ideas where to get a decent piston? I'm mostly seeing Little Red Barn. I imagine I should replace the seals as well? Has anyone found a good reasonably priced source? Any other tips? Ive heard that I need to open up the muffler. Ive got it mostly torn down now, just hope I can remember how to put it back together. Also, I'm coming up with several part numbers for the piston and not sure which is correct. P021006150 (NA) ,P021006152, P021006153. Any ideas?