Outer Limits 4x4 Board

2001 Holden Astra;
Electronic speedo is working intermitantly, it always works first up but then after approx 10-20 km stops working. Is getting slowly worse, it used to flick on and off, now once it stops it stops until it isn't used for several hours.
I am thinking that it has to be a sensor, most likely from the transmission (auto) however I can't find the bloody thing.
Anyone have any idea's, or even a better explanation as to why's it's playing games?
thanks
Pony

Most likely a faulty/dirty transducer (speedo sender from the box).

Has it thrown an engine check light?

Any other lights come up on the dash when the speedo drops out (eg: ABS light)?

No mate;
No engine lights, nothing changes apart from the stereo gets a bit softer, as in less volume, nothing else.
Any idea what the speedo sender would look like?
Thanks
Pony