I had a nice response, but...
oh well these things happen. I'll try to rewrite.
The exhaust pipe and exhaust leak will not cause low compression (the answer to your original question yesterday). The leak, however, may be the result of a blown head gasket. Your leak is in the area of #4, #4 is the cylinder with low compression, and is the gasket is blown bad enough you could be losing compression to the outside of the engine (the leak).
Are there any other signs of a blown head gasket, oil in the water or vice versa? If it is just the head gasket, the head will have to come off, might as well have the valves done while you're in there.
Definitely not a 8.5K job. Find a good independent in your area.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.