New, stainless steel fasteners have arrived from England.
I wanted to upgrade the fasteners holding the chassis to the body, so I picked up a set from a gentleman on eBay (Member id: dcmotorsportuk). Some people sell these kits and include the rectangular mounting brackets, but I decided to keep my originals, and just clean them. The bolts could be cleaned too, I suppose, but some of the broke anyway when I was taking them out; I think the stainless will give me a longer-lasting, rust-resistant fastener.
Also, the engine tin bolts just seem to deform when you take them out. Straight-slot heads are tough when they get rusted. So I also picked up a set of engine tin fasteners from the same eBay seller.