I agree you are on target. The speakers have paper/cellulose cones and just deteriorate over time. They aren't that great to start with.

Sunroof you are probably spot on, my experience is that if the roof gets used and properly lubricated they are pretty robust, however I think the majority do not get used and the felt dries/lube gets gummy and strains the system causing failure or finicky operation, dealing with this now on a 500SEL.

Washer, spot on, check the orifices and go backward to the pump.

Headrest, may be a bad switch, possibly a short, or the gear may have separated from the rail, remove the seat back with the two screws on the bottom of the seat back and pull the panel straight down. The mechanism will be right in the middle of the seat and easy to inspect.

Good luck!

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1981 300TD
2005 C55
2004 E500
1999 ML430
1992 400E
1998 C43
2001 SL500
1988 300SEL
1986 190E 16V
1991 190E 2.6