I have noticed that while driving my SEC, there is a rather alarming amount of heat coming from the center console area, around the radio and shifter. It's heating everything up to the point where only hot air blows from the AC vents when the AC is on, and I am smelling a bit of exhaust gasses. The metal ashtray literally gets too hot to touch, it will burn you.

So while I was underneath the car changing the o2 sensor, I took a look at the center console/driveshaft area, and noticed that the driveshaft and almost all of the driveline parts have been replaced and look new. I was, however, shocked at the condition of the transmission tunnel...there are gaping holes in it and it looks like the car broke a flex disc at some point...

Looks like this, but not quite as bad:



On the dieselgiant tutorial, they use "caulking" to secure a piece of sheetmetal in place. What kind of caulking are they referring to, and how would you go about fixing this problem?

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Current cars:
2000 ML55 AMG, 174k miles
2003 C240 T-Modell, 202k miles
1995 S320, 207k Miles