Presumably, you rubbed some oil onto the rubber gasket before fitting the new filter?
Leaking OE filters are certainly not unheard of. I had a genuine Ducati filter start leaking on my Evo, (but after a couple-of-thousand miles not straightaway like yours). Tightening it failed to stop the leak so I replaced it with a K&N KN-153, which has a hexagon on the top to enable accurate tightening, (to 11Nm as per the manual). No leaks since and I'm about to fit my third K&N.
http://www.ukmonster.co.uk/monster/s...t.php?p=541955
Whether you go for K&N or OE, just make sure you get a genuine example as there are cheap counterfeits out there.