i do know that running w/o gearbox oil in a minarelli engien will wreck the clutch. of course, it could be other things. but i remember reading (and have some confirmation above) that that was it.
the avanti is the new garelli ... so it should take the same, sae 30 motor oil (non-detergent). but if someone knows differently, let me know. check the owner's manual. it should say.
during the break-in period you should probably fill and then drain it after maybe a month or so and then refil it again. i refil mine at the stat of each riding season (sometimes twice a year).