So... after the 2307 mile round trip, without breakdown, the gearbox had began to make even more noise than it originally did.
The time had come to replace it with a spare in order to strip and investigate the problem.
Removing the gearbox with engine in situ
Old and replacement
One problem discovered. Bearing 'retaining rings' on the tripod bearing have worn through for some reason, allowing the roller bearings to come free.
Possible cause? Maybe poor quality bearings as bought as part of non OEM UNO driveshaft?
Reason?
Because the driveshaft is at an increased operating angle, the rotational force from the driveshaft does not only result in a radial force, but also acts along a second vector, longitudinally. Pushing the bearing race against the retaining ring and wearing it out. Thoughts?
Drivers side driveshaft checked and has no obvious wear
Also absolutely no contact has occurred between main tapered gearbox bearing or modified flange and driveshaft, confirming the raised geometry is all OK
Additional problem found was not enough additional shims were added to the near side main bearing to account for the difference in depth of the fiat 127 gearbox flange used.
Flange depth of panda measured as 12.6mm. 127 flange measured at 11mm
Additional 1.8mm shim to be added from removed gearbox.
