15600 miles on my 2005, just replaced the cylinder base gasket, replaced the intake valve in june 2012, I saw the origional honing marks on the cylinder wall after 15000 miles, good for another 15000 miles, runs great.
Fairly simple,get a service manual,remove seat, tank, carburator, exhaust header pipe,head, and cylinder. Remove and clean old gasket and o ring (note : clean all gasket mating surfaces extremely well) then replace with a new gasket and o ring for a 2010 or newer and reassemble everything.How much effort did it take to replace the gasket..OMM.