I would run fast and run far from any equipment that had been submerged in floodwater.

Big difference between dropping a tractor or a pickup through the ice and filling it with nice clear cold water and having it fill with silty water. The former can just be drained, flushed, and you're pretty sure it will work for a long time. Fill a transmission, crankcase, or diff with muddy water and you really need to completely dis-assemble and clean or change every bearing and seal.

After the last big flood in the midwest, some local machinery and truck jockeys imported what came to be called "Flood victim" outfits. Not good for the un-suspecting buyers