One potential entry point for water is the area where the vacuum lines for the door locks (and wiring harness for the electric windows/mirrors) leave the cabin and enter the door. This area is sealed by a bellows-style rubber boot that ends up cracking and is rarely replaced. It can be done without removing the door. The front door boots on my car were cracked but the back door boots were still intact. I guess they survived longer, as the rear doors are used less often.
The front boots for my car are part number 107-821-00-97. I obtained them from the Mercedes-Benz Classic Center USA in Irvine, California when I visited there in February 2014. With tax, the pair cost $11.47. Their phone number is (949) 598-4850. I replaced the DS boot August 2014, but only took a “before” and an “after” picture. When I replaced the PS boot in November 2014, I took a bunch of pictures to make this DIY. This car is a 1978 W116 300SD with electric windows but the procedures are generally applicable to other models.
Basically, the wiring harness is removed from the door (the vacuum lines in the door stay in place) and then the replacement boot is fed through the hole in the door. The new boot is flexible enough to be manipulated into place unscathed when the wiring harness is out of the way. There is no need to use lubricant to install the boots. Periodic use of a good protectant will keep your new boots supple for a long time.
The steps I followed are listed below:
1) Disconnect battery
2) Remove door panel and vapor barrier
3) Completely remove door check from door (this is a good opportunity to re-grease the door check)
4) Remove old boot from door and cabin (side-cutting pliers help to remove the boot – just don’t cut or nick the vacuum lines)
5) Disconnect power window wiring harness from junction block in door and pull harness out of door
6) Disconnect vacuum lines from vacuum element in door and free vacuum lines from door clips (remember which line goes where, or take a picture before disassembly)
7) Feed new boot over vacuum lines and through hole in door, (slim hands are helpful), (first tight spot by window motor – work it up slowly, push from below , then pull from above – just take your time), ( second tight spot at hole in door – a gentle tug on boot with pliers reaching in the hole from outside, while simultaneously pushing the boot from inside of door, is what I did)
8) Feed power window wiring harness through boot and then feed harness back into the door
9) Correctly route wiring harness and reattach wires to junction box in door.
10) Seat grommet end of boot into hole in cabin (a bit tricky as it wants to pop out of place, I held it in back with two fingers and gently forced the last bit of the grommet end into the hole with the rounded end of a hex bit driver – it took about ten tries before I was successful)
11) Seat grommet end of boot into hole in door
12) Correctly route vacuum lines in door clips and reattach to vacuum element in door
13) Install door check in door, slip on rubber hinge cover, then grease and re-insert pin in hinge (don’t forget the two nylon bushings and the retaining clip), and seat the rubber hinge cover
14) Apply adhesive to door and then reattach vapor barrier
15) Attach door panel and door trim pieces
16) Reconnect battery – all done!
Hopefully this pictorial has been helpful.
