I don't know about your specific engine but on my 450 slc the tensioner just bolts to the side of the block and can be replaced w/o going into the engine. I would assume that the tensioner was renewed with the chain. Certainly at $2,100 it should have been. Replacing the unit is not very involved on the 450slc since everything is external. Ask the dealer why they are using crap parts that only last 40k miles.