This seems like an unusual question, but the passenger rear floorboard is collecting water. I am not sure where it is coming from. It seems to return after removal and rain is not the source. I noticed there are some things on the floorboard under the black foam mat, one sticks up from the floor and the other looks like a cap or something, I am not sure what they do. Anyone encountered this? I was told it could be from the air conditioner, which seems odd given the location.

Had this exact same problem with my '83 380SL. A hose under the dash (passenger side) had become disconnected, and when air conditioner was on, the water was draining back into the passenger compartment. As I recall, the fix was pretty easy and did not involve removing dash.