As they say about Italian cars, if it aint leaking it needs more oil. Topping off every 1000 miles is not bad at all, pretty normal. As long as oil isn't leaking onto anything vital (belts, alternator, etc) it really is just a matter of how often you like to add more. The only real problem to leaking oil in non vital areas is that it makes a big mess. You're nowhere near a problematic leak though so don't worry about it. Ferrari uses nikasil liners too since the 308 QV (mondial 4v too) engine which to me seem inherently prone to leaking some oil too which would account for some burn off and a need to add more oil once in awhile. The liners never wear in, so although they are super smooth and tough, they can't seal to a ring as well as when the liner breaks in with the ring. Just my $.02