shit man ya have the oil... use it IMO I wouldnt use a synthetic oil in a Guzzi if I had to buy it, a semi is fine.
never heard of a filter unwinding, if it happened then some on shouldent have been farking with the bike to start with and what if the hose clip comes loose?. most add a molly slip to the box and diff, I never have, never noticed any differance.
Other than what ya have said, tappit clearance check all else if going well leave alone.