I had a new left front fender put on...nice job. 1989 300te. Is there any rustproofing I should do, over and beyond what they "said" they did in the shop? What are the "rust areas"
of the 300te? I would like to keep this car "forever". It is salt time here in the Northeast.

What did they say they did in way of "rust proofing"? MB uses a wax based rustproofing. If the inside of the fender is coated in undercoating, there isn't much more you can do.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member