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There is a key on the crank gear- and a keyway groove on the crankshaft. I would ask to see the crankshaft to verify that the keyway is damaged. Typically what happens is the bolt loosens, the gear gets loose, and then the key shears off the gear. In the meantime, the looseness of the pulley hammers on the keyway.
I would see if you can get a new crankshaft for it. While it will require dropping the transmission to install, it's really not that bad as long as they have a hoist that can lift the Rialta.
I've never looked at the parts film, but despite the engine code being slightly different between the full campers and the other 2.5 Eurovans from 92 up, I bet the crank is the same in all of them (you could have a dealership parts department verify this)
Your oil consumption may just be due to the old, dry valve stem seals cracking and leaking oil.