I had to replace the freeze plug on my 300TE.
The above is correct about not using the correct Zerex G-05 coolant. That or MB coolant is the ONLY coolant you should be using -- along with distilled water.
6hrs labor? Gotta be kiddin.... You can access it, albeit a little tricky without removing anything. Its probably leaking at the same one in my pic (left one).
Here's where it is. You can see I replaced it. Ignore the arrow
