Lost compression in '77 280E (W123)

My 280E, with 286,000km on the clock, is idling a little rough when the car is at standstill in Drive. As soon as the revs pick up, they smooth out and the engine pulls fine.

The M110 engine was reputedly rebuilt at 210,000 by a previous owner, but a mechanic has now diagnosed uneven compression. A compression test revealed that #6 cylinder is down to 115lbs compared to the rest at 175/180lbs. On doing a cylinder leakage test, compression appears to be leaking past the rings.

What is my best course of action here? Can I keep driving the car for a while? Or am I looking at a full rebuild of the engine, with new pistons and rings and so on?

Or could there be a simpler, less expensive solution to this impending problem?

The car is not using massive amounts of oil, but has started to steadily lose a little coolant. I don't know if this is a related problem.

Any advice will be gratefully received!

Chris