I have a 1998 Disco 1 and the front fog lamps have fallen to bits- they're the ones which are set into the lower part of the bumper not bolted to it. Looking for a replacement set.
On both of mine the glass front has detached from the back case, and the incoming water/dirt/general road crud has basically dissolved the innards. I think they're supposed to be joined in a (theoretically) watertight manner.
I was also considering just removing the lamps and filling the space with some suitably similar DRLs instead.