Very interesting subject.......I will try not to drone on too much....but.....for most of the ownership of my 74 350 Mk3 (until about 15 years ago) It has had a real and sometimes quite dangerous tendency to front wheel wobble at speed/potential to tank slappers, but all only under very particular circumstances........at speed (70mph or over) on a rising road at the apex of a sharp left or right hand corner when the front end would get a little light off it would go. I tried everything I knew to fix this all to no avail .......tyre pressures, different tyres, fork oils of all weights, different preload on forks, variably dropping the forks through the yokes, wheel alignment, swopping from the odd 19" front wheel rim to a normal 18"(the wheel size change helped a little but didn't cure it).
In every other respect the bike has handled flawlessly and has been (and still is my favourite motorcycle of all time) so I kinda gave up and fitted an hydraulic steering damper which obviously didn't fix the problem .....but like a painkiller tablet it hid it from me. About 15 years ago at an autojumble in Dublin I couldn't believe my luck when for very little money I managed to buy a set of genuine Ceriani 35mm grand Prix road racing forks (and I mean real ones not repro) these were almost unused and had been removed from an American import Triumph flat tracker.
I stripped them, cleaned them, fitted new seals, and put them on the front of my 350.......the overall general improvement was so noticeable that I tried removing the hydraulic steering damper......and guess what the wobble/tank slapper was gone never to return!

at any speed or circumstance, I without doubt spent a bloody fortune on sets of tyres to cure my wobble and it was the cr*p Marzzochi forks all along.
Cheers,
George
P.S. My 250 desmo has never exhibited this problem!