Fellow 560sl owner
Just find a reputable mechanic in the area, have them pull the valve covers and get a look at the chain and rails condition and measure measure the chain stretch. Shouldn't be more than $200 in my opinion. I think the consensus is that if the chain has more than about 5degrees of stretch and the rails are reddish brown, then replacement is called for.
Agree with looking at the Pendelski pictures if not just to familiarize yourself with the terminology. The problem with these chains seems to be that they are so long and go in and out to so many different sprockets that if it gets a little stretched and jumps a tooth or gets too loose, it can break off a chip of rail, in turn it gets stuck in the sprocket, causing the whole chain to come off with the motor running, which causes all kind of havoc with the valves and pistons colliding. Not a good thing.
The rails which act as guides to the chain are hard plastic and wear out and become brittle over time and can break. There is also a chain tensioner that looks like a really big bolt at the front of the passengers side near the frontmost sparkplug. It also keeps the chain somewhat tight and on line.
Check out the pendelski and read the comments about the tensioner and the rails and how to measure the stretch and at least you will be able to understand the mechanics lanquage.