Once I'd removed the black plastic discs, everything came out almost as the manual described.

The black rubber weatherstripping was held in place around the base of the wiper arm by a metal strap. I had to push the lower circular portion of the rubber under the lip of the air inlet cover in order to remove the cover, then unbolt the wiper assembly and the wiper motor came off along with the weatherstripping. I should have taken photos.

Typically though, the blower motor seems to be fine. Once I'd removed the blower motor housing, I tested it and heard a loud squealing from the motor. I disconnected the power cables to the motor, was able to turn the squirrel cages by hand, retested it and heard nothing. I then reconnected the power and tested a final time, and it started working (much to my simultaneous frustration and surprise).

So, my brand new Behr blower motor is still in it's box, waiting for the day it's called into service. In the meantime, I'm going to take my car out for a drive, now that I have air conditioning in it again. With one job off the list, the next is a good wash and wax at the weekend, and then on to tackling the power antenna that seems to be reluctant to extend.

As for the wire harness and head gasket - no, I haven't. When I was shopping for a Mercedes several years ago, I came across the head gasket issues in the 3 litre engines (103?) and decided that I was much better off with a slightly newer engine (104) that didn't have those problems. I've been bringing it to the dealer for it's major services and head gasket and wiring harness issues have never been mentioned, raised, or noted on any of the service sheets. I'll certainly inquire when the car's in for it's 150K service though.