My right door on my 91 SL has rust underneath, toward the front. There is no rust anywhere else on this car, and it spent its entire life in California - LA area. Why would it rust in that spot? How would you fix this? Replace the door, or take it off and weld in a new piece? Will all 129 doors fit all 129s?

And while I'm at it, any leads on later model taillights for my 91?

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport