Take aluminum tape and seal up your exhausts at the the ends, then jack the car up from the back and supprot it safely. Start the car. If you reach your hand up around the muffler, you may notice that is has a hole or is scratched, My wife hit a big rock with our 400E the drive shaft bounced up and punched a hole in the exhaust pipe right above it. PC-7 seems to work well to stop the holes.

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles