Definitely replace the three upper guides, the tensioner and the tensioner rail. I wouldn't worry about the two lower guides on the engine block, they are quite robust and are a pain in the ass to change, especially on an SL. You must either pull the engine or drop the subframe to get the SL specific one piece cast oil pan off.

__________________
Chas

Had a 380SL, 450SL, 380SEL, 420SEL, 500SEL

Got a Euro 500SEC right now.