dont know of a fix but i have the same problem on my 2000 triple. but since my speedo cable broke for the third time and rounded out the brass bushing that holds the cable top, i have been using a bicycle speedo for over 1 year. my speedo has just over 20800 on it my bike speedo has about 10000 on it. triumph want $1000 thats right a grand for a new speedo cause they said i have to replace the whole unit. i think i can fix it cheaper but have not had time to yank it apart. winter is here almost. perfect time to start pulling the bike apart. when i have it apart i will look at the light and see what can be done with it?
mike