While parts is parts as they say WP only uses top quality OEM gaskets, seal and o-rings when building your baby.  On high end engines this is very important for tolerance alone.  Many aftermarket companies, although many are good, don't always continue to manufacture the product or make changes in product tolerance over the course of some years.  Well, by the time you may need a rebuild or re-ring you may not be able to get those aftermarket products any longer where as the OEM shelves are typically full for many years to come.  In some cases WP has had to manufacture in small quantities specialty fixtures to mount oil seals that are NA.  This is not a problem for us.

When it comes to the fire eaters, pistons that is, WP prefers Wiseco.  Many two-strokers have been given false information about Wiseco in the past and if you're not a fan of their product let me help you out with your confusion.

Wiseco is the most widely used aftermarket piston in ALL fields of motorsports in the USA.  Forged from high grade silica and aluminum alloys they provide maximum strength and longevity with minimal flex and expansion rates to overcome  the infamous "cold seizure" problems many face with cast pistons.

A super high quality piston at a very reasonable price is what you get every time.  Don't let some hack tell you they'll only seize your engine, you have to know what you're doing to fit them.