1990 300SL timing chain tensioner
 

Does anybody know the procedure for replacing the timing chain tensioner on 104 engine?

Yup. Take off the end cap, it will be under a bit of pressure. Then remove the guts of it and remove the housing from the head. Screw in and torque the new body, then put the new guts in it (pointy part with the lock ring (it only goes in, it doesn't back out), the new spring, then the cap sets on the spring and yo really need to muscle and screw this thing to the new housing. There should be a new sealing ring with the housing and also for the cap. I'd recommend disabling the ignition system (remove coil wire), then crank the engine for 10-20 seconds to build up oil pressure in the tensioner before letting the engine start.
Gilly

Thanks Gilly, This seems like a no-brainer. Is there any chance that the chain cuold jump a tooth on the sprocket as long as the engine isn't cranked over without the new tensioner installed?

No, I don't really see how that would be a possiblity. Take great pains to make sure the engine isn't cranked though, such as disconnecting the battery cable, whatever works best for you.
Gilly

Thanks Gilly, I guess it's time to order the parts...