2000 grit wet and dry with WD40 will remove surface rust without damaging the chrome.
But you must polish the fork at 45*, not up and down or straight round. (cross hatch like honing a bore)
Also, if the oil seal (not the external dust seal) doesn't reach said point where rust is evident, your seals will be safe.
Failing that, a trip to the local bearing shop with the old 'O' ring will net positive results.
Guzzi don't make forks, they use Showa's on the GRiSO, standard item on 50% of Italian and on most Jap sports bikes. Guaranteed to be a standard metric item, would bet me left nut on it but Centre Bet says it has no value.