My '07 500 has about 36k miles. Mostly stock parts. The few aftermarket such as Dr. Pulley sliders and one aftermarket belt, I am convinced OEM is better overall. Unless, you are racing, or something similar, and are willing to perform extra maintenance.
All the OEM parts have lasted longer. The most recent failure involved the D.P. sliders. The scooter was still running when I pulled into the Austin dealership. One slider was broken in two, another chipped, all worn to the point where the ramps were leveled, and a couple of rivets were rattling around for good measure. The scooter arrived under its own power saving $75 in tow costs.
I have my own theory as to why so much damage was done - more than I was aware of - which is a topic for another thread.
I think the OEM is good, long lasting stuff. The seat's too hard, but the cover will probably last forever. Now I have a custom seat with ortho foam and a good lookkng two toned color scheme. Other than that, OEM is my preference.
What about yours?