If tesnioner is cocked then you need a new tensioner. If the shock quiets when you put pressure on it then the bushings are shot and you need a new shock. After all that, you might as well put on a new belt as well.

To add to what BusyBenz said, put a tire iron or long rod in the ~12cm hole of the pastic pivot that holds the top end of the spring. Remove the nut that takes a 13mm wrench at the end of the bolt that points forward from near the fuel filter. Tip the rod slightly CCW to release tension on the bolt and pull the bolt back so it clears the plastic pivot. Now tip the the rod CW to release tension on the spring so you can unhook it from the pivot. It's an alternative to "pulling like hell" like BusyBenz did

FWIW, I'm able to replace the tensioner in my SDL without pulling the radiator or fan.

Don't wait too long to do this job. Search the archives for DaveM/gsxr's adventures in replacing a timing chain cover after a bad tensioner tore loose. AFAIK, the engine is out of his car and he's still not done.

Sixto
95 S420
87 300SDL