Years ago (literally early 70's) Lucas used too make a lamp 'service kit', there was a single and dual contact version. Small fibre disc and a spring, the fibre disc getting wet and failing was a problem back then and nothing's changed. Just a few pence and a clean up of the lamp body would save pounds if they were available today.
I made my own discs from a sheet of black plastic used in home aquarium filter tanks, a bit of a fiddle but about 15 min with a Dremel each was a nice garage job with a coffee and the radio on ;-)
