ok shim in. Was a bit tricky getting the plastic off around that area due to the 12 years of rust buildup on the screw threads. Taking the cap off easy, taking the C-clip off got that after a few minutes using small electrical screwdrivers. Putting the shim in was easy but getting the clip seated again took a bit more work probably 10 minutes as I had to slowly push it back in with the flat side of a screwdriver head.
Took it for a quick spin in the snow, that goodness for winter tyres and did not hear any whine noise from third. Tomorrow will be the big test as I drive to work and during the day etc.
Sounds like the forum may have saved me a recon of a gearbox thanks to everyone.
David