speedo problems

["Ed " <mcji6es2@fs1.me.umist.ac.uk>]

Hi

I own an '91 2.2 100. The speedo shakes around erratically at all speeds 
indicating about 2/3 real speed and recording about 2/3 the real 
miles on the odo. I've had the dash out but was shocked to find it 
was all electronic - and I'm frightened to have a fiddle. When I tap 
the speedo it some times shoots up to the real speed. Any ideas on 
jow to fix it? Do ya reakon I'll have to buy a new one? -Do ya know 
if it can fail an MOT for this problem? Will audi breakers supply the 
part since I don't want to pay VAG prices?!

Thanks for any help,

Ed