Wow - there are no words for leaving the chain in the pan. Probably fell in and responsible party hoped and prayed that it wouldn't cause a problem. Being heavy, it just sat in the sump until you found it.

I've seen those wing-nut oil pan plugs before and believed them to be an "emergency fix" until such time as the pan can be either repaired or replaced. I once changed oil in a 50-something Chevy that had a hard rubber plug driven in the hole. When I got it out the threads were fine and I as able to use a new stock plug. Previous must have lost the plug and found something that would work.

Go figure... Glad you able to fix it Ken.