I just adjusted my valves on my 1973 450 SL. The car has 183000 miles on her. I noticed the timing chain seems a little loose at certain spots on the rotation during the valve setting. There are spots where I can pull the chain away from the upper rails and touch the head casting. I have read some threads that say the Chain Tensioner is supplied oil to create pressure on the chain. Is this correct?? If that is true, then can someone tell me how to check chain stretch on the car using the crankshaft pulley? The guides I can see with the valve covers off, all seem ok. I am wondering if the chain tensioner is not functioning correctly. Previous original owner says she had "valve work " done some years ago around 145000 miles, but can't recall just what was done.

Thanks,
Mark