temp warning on '88 90Q

[studentper]

three problems

1. the temp warning light is coming on, and it's definately not overheating.
i checked the resevior and then checked the switch under the big tube coming
off the radiator right where it connects to the engine--it's covered by a
rubber sleeve that holds all the water/antifreeze/crap that drips.  the
switch was sitting in a small puddle of stuff.  is this the problem?  how do
i take this switch off/out to clean it if it is?  is it expensive to
replace? is it critical to anything?

2. the chain thingy (i know, bad description) on my sunroof is broken
somewhere.  the great guy who fixes my car doesn't want to touch the
thing--is there something i can do.  i am a little wary of messing with it,
since the thing is broken closed and not leaking.

3. is there a way to get to the light inside the radio display?  it's the
standard radio/cassette, but the display is burnt out.  i can't figure out
how to unscrew the thing, even when out of the dash.

thanks for the help--bryan, 1988 90Quattro--great car by the way, knock on
wood.