porter/cable 6" random orbit sander (7336sp)

I would love to fix my old 7336sp. I have purchased a new one because I need it to do my surfboard repair.
At first I thought it was just the brushes. When I got the new one I did some part swaping and came to find that it was not the brushes or the variable speed roller switch.
What is wrong with the tool? It seems to fluxuate in rpms. It also seems as if the motor is producing more heat than normal. I ran both tools new and old next to each other and the old one definitley is much weaker.
If I can get some good direction I would love to fix the old one unless the parts out weigh getting a new one.
Thanks for any advice
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