We changed and swapped the vertical gyro's and other spare components around that control the horizon's and the effect was the same. So, I concluded it was the instrument that was at fault. Because roll and pitch only happens in flight it became clear that the flight instruments, particularly the artificial horizon's would slowly seize up with ground use only.
I removed the instrument from the panel and dismantled the casing to find the mechanism's to be very stiff. With a good clean they freed up nicely and the instrument is ready to be refitted.
As far as I know this is the ONLY totally working MFS system fitted in any of the surviving working V Bombers so, it is historically important to keep it working. Luckily we have a number of spare components. But, we are always on the look out for further spare parts.We are fortunate to have the correct MFS test set that plugs into the aircraft and we have run the correct checks a number of times.