Thanks deliverance, I think most of what you refer to was after my time, so was not aware they were used 'in anger' or more aircraft were 'converted'.
I was on the 16 FI wing change team 91-95 and remember the issues that some F3s had with nib and wing cracking caused by wing fluttering due to having no dampening from outboard pylons and stores, this was found when using the aircraft in a different role than the one it was originally envisaged for (I think some was playing at low level), hence why we were told that it was a trial to confirm this, which it did, apparently.
During my time on the F3 OCU at Coningsby (86-87) was when the problem first appeared, if I remember correctly, and the lower wing nib panels had to have the stringers replaced with better made ones to try and stop the cracking, before sorting out the actual root cause and getting rid of that, which they eventually appeared to do.