Yeah, it happens. Usually if your oil content is too high.
Here's the skinny... the gasket you're going to want to order is one of the super thick exhaust gaskets. They seal great, and they cost next to nothing. The bad part is that I'm like 99% sure it's made of pure asbestos. It's fine to use, just don't pulverize the gasket and make it shoot out little fibers and you'll be OK.
And, solve your excessive oil problem for good. Get you some opti2 stroke oil. It costs a little more, but the cost is offset by less maintenance and longer life, as well as less oil required! You can't lose with opti2.