As for the exhaust smell/leak, also check the exhaust manifold gaskets. Do you have a little ticking on cold start-up, that goes away once the engine is warm? If so, sounds like exhaust manifold gaskets. Word of caution, it is possible to installed the gaskets 180* out. This is most likely on #3 and #6 exhaust ports I believe. The last hack to work on my 560 (before my ownership) did just that. The gaskets do seal when installed 180* out, but quickly burn through. Worth a check.
'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.