My '96 Celeb had exactly the same as you describe - it was The Rot. The windscreen on the F/L cars was bonded-in, so the chances of leakage through that pretty much zero. I hate to say it, but cut -out-and-weld is the only solution.

I bought a pair from JCP about two years ago. The XJS one has lost its chrome already, and I don't polish it!

I have the same problem. I would look in the air-con section, but of what publication/forum/site?

I have exactly the same problem on my '96 Celebration, and had exactly the same reaction from Stratstones at the last service! I have had the plug out, cleaned and replaced it with no improvement. I have checked the wiring diagrams but can see no function, other than low brake fluid for this warning...