Jason Hall here on the forums has repaired a few R cases where the balancer bearing goes. They bore them out and sleeve it with a proper sized sleeve. He is in Michigan also.
I have peened the cases with a center punch if the play is minimal and used red loctitie, but I dont know exactly how long that will last. The raised area from the peening will make up small tolerances. However, if you bought a used balancer, I am willing to bet that the bearing is bad anyway. Those can be replaced. Just mark the gear to the shaft with a grinder and press the gear off and the bearing slides right off. Just make sure you keep the gear oriented to the shaft for the balancer.(In time).. The bearings are on ebay for like 20 bucks.
As far as your seat, you can remove the entire cover and it will go back on pretty easy as it is formed to the foam. The best way to fix the studs is to press them out of the plastic, then make a steel plate with new bolts welded on, to pass through the pan then set your foam back on. If you are careful, you can also heat the pan with a heat gun and peel the OE studs out, and weld washers to new studs and heat the pan again and slip them back in the molded slots and use a plastic welder to resecure them. But a new bracket with bolts welded to it, is a better repair.
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