You might try adjusting the valves. There are special tools for this but it can be done without them. It just takes longer.

I say this because it sounds like two problems to me. The low compression cylinder has a burnt valve. Nothing will take care of that but a valve job.

Is there a lot of smoke when you start up that then seems to go away? If so you have worn out valve guides. These are normally replaced during a valve job, so that might cure everything.

If the engine is shot you would probable do best to buy a used one. A rebuild is recommended by Mercedes every 250,000 miles, but a well cared for (and I do mean WELL cared for) engine can do twice that.

Check the valve adjustment. I bet that one cylinder is out of adjustment.