So make sure the gaskets are fresh and replace them at any sign of oil leakage. As for what pipe to buy my suggestion is to do your homework. Read the dirt bike magazines and call the pipe companies. A lot of people buy a pipe for the wrong reason. When you change your pipe you are altering your power.
Some pipes are low end some are mid range and some are top end pipes.
So you need to make a choice on what will suit your riding needs. I own a 1996 Kawasaki 1500 Vulcan. It was running bad, so I checked the plugs. Changed them and 10-15 miles later, the same thing. I'm getting 15 mpg.