ST3 speedo

The speedo on my ST3 has packed up -again.It first happened in Germany 3 months ago after three days rain. I took out the printed circuit board and dried it but was not even damp. It still did not work. Then two days later it started to work fine again.It has stopped again. I am told a new board costs £400.( can this be right ? ) Could it be the speed censor which I am told is on the back wheel.Is this replaceable? the workshop manual does not seem to mention it.
Any ideas would be greatly appreciated please. Are there any electronic firms out there that can do repairs, if it is possible to repair them.
Thank very much Philip Boobyer

Reprying to my own post. I have replaced the speedo sensor and all appears to be in order as on a very short test ride the speedo is working again
Cheers Philip Boobyer