forgot to mention I had oil in the ignition coils as well on the right side (just replaced the valve cover and plugs to fix that). seems to point to some issue on the right side of the engine. I assume it might have to do with some pressure backup issue. It looks like you have the same problem.

What brand convertor did you end up going with?

I also researched how to test failed convertors and saw some interesting information about testing with an IR temperature sensor (which I already have). I will test tomorrow.

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2008 S550
2010 GLK350
1997 E420 (retired)
2005 CLK500 (retired)