I have a 1985 911 and have a long history with it. Generally I don't have oil leaks (173Kmiles) unless oil return tubes or cam oil feed lines are shot.
So if something is wrong it should be fixed but you may be talking about general leaks.
BUT I'm running 20W50 dino. I have considered switching to synth but leaks can become a problem. I would guess a 2002 requires pure synthetic which is more prone to leaks, even 15W50. A freind of mine told me he uses 10W30 synth in his late model.
Use only the recommended oil weight. I would research different brands. I 'think' I read Royal Purple synth leaks less in our application due to its base stock. Also additives in the oil may have different effects on seal swelling. Unfortunately gotta' do your homework as oil can be very complex topic. I would not consider a separate additive for this purpose.
See
http://theoildrop.server101.com/forums/ubbthreads.php
which is bobistheoilguy (BITOG) forum.
Also
www.rennlist.forum
Look for practical experience with your model and various brands.