Jerry,
If you follow all the posts here, and put two and two together, you'll understand the following--
1) Water getting into the trunk is a common problem; often unknown until one lifts up the mat. Even today many have issues with it.
2) Because of (1) many trunk (boot) floors have rotted out.
3) Some poor-quality sheet metal work by tinsmiths (er, "body men") is often hallmarked by the profuse use of sheet metal screws.
I wish I could show you a photo of a 1966 230SL I went to look at around here for a friend last fall. The trunk and underside were littered with sheet metal screws holding in patches of new metal.
Often times the screws are then covered with copious amounts of underbody coating or tar.
Michael Salemi
1969 280SL
Signal Red w/Black Leather
Restored