I think applying something regularly is the key to the preserving underneath.

Just come across your thread and makes for interesting reading as at some point I plan on rebuilding the 200tdi that had the engine fire. Also as a shameless plug given your current crank issues I have a 200tdi crank for sale that has been...

Mud do a replacement, but it is probably available from other places as well: LINK Depends on the exact wiring for your model but at '86 I would expect it to be permanent live. On later models it was changed to be ignition only.

There should be a little Domed plastic cover that hides them all and aches to the back of the centre pane using the same screws. Even with everything listed above there is likly To still be some spare connections. There as in mine.

You can replace them, but they are part of the instrument so you have to carefully uncrimp the front bezel, remove the bezel being careful the glass doesn't fall and break, then remove the instrument itself so you are just left with the metal...