Whenever you replace a nut, bolt, or fastener that isn't in a critical safety area i.e. suspension, brake, etc.... get the cheapest one from the local hardware store. This will ensure a rapid coat of rust, just like the factories use to attach the trim of cheap travel trailers. The dissimilar metals touching each other will wreak additional havoc. And don't be afraid to experiment beyond the realm of the simple hex head nuts and bolts- get some with wings, allen heads, etc.... there's all kinds out there. Nothing sets off a clutch/transmission case like a contrasting array of dissimilar fasteners all holding the same part onto the engine. We used to call rust "Poor Man's Lock Tite".