Don't use a pressure washer or you'll probably end up with water where you don't want it to be, i.e. inside the crank case, cylinder, etc. High pressure water tends to make it's way through the tightest of gaskets and fittings. Foamy Engine Brite, a garden hose and a little elbow grease is all you need.
As for your pipe leaking at the cylinder, pick up a billet aluminum o-ringed exhaust flange from ESR or anyone else that makes them and your problem will be solved.
Current Ride (Purchased new in Oct. 84) - 1985 Honda ATC 250R w/ ESR 310cc big bore kit
Wife's Ride - 2009 Polaris RZR 800
Kid's Rides - 2009 Yamaha Raptor 700, 2008 Yamaha Raptor 250
Former Rides - 1975 Honda XR 75, 1979 Yamaha IT 175, 1978 Honda ATC 90, 1980 Honda ATC 110
got sand?