For my tuppence worth can I ask if you have managed to lift the front wheel completely clear of the floor ? The reason I ask is that many moons (1967) ago I had an A10 outfit that suddenly started handling like a bag of s*** from being just normal, did the same check has you did , same results, really scary , lifted the front end and removed the wheel ,turned round and the fork leg slid down the stanction , the circlip had gone the way of the gods and must have destroyed the bushes has the leg fairly rattled on the stanction ,hope this isn't the case but ,well, check it out regards BobH