You will probably have to to swing ancillaries out of the way and perhaps the cooling fan and radiator to gain enough access to pull out the slide pins which secure the rails. It's been 5 years since I did this on my 560SL, so the details are a bit hazy.

The tensioner on the V-8 is non-ratcheting so it is just unbolted and rebolted with a new gasket.

__________________
as ever
Paul

1989 560SL
1987 300SDL
1987 300TD
1983 BMW 633CSi
1972 280SE 4.5