If I recall correctly, I've had the same issue some years ago, so I had to scratch my head a little to fix it.
The oil filter element cover has 3 screws on the filter side and 2 screws on the collar.
The first screw set is threaded on the strainer cover, you have to tighten them as required - see above.
The second screw set (collar) is threaded on the crankcase, NOT on the strainer cover (it goes through both covers). In case you tighten them incorrectly, the strainer cover AND/OR the filter element cover may warp enough to get some oil leak.
(edit) I'm not quite sure about which screw set goes here or there, but the general idea is that some screw are threaded on the strainer cover, others are on the cranckcase.
Edited by JBX, 03 May 2018 - 01:31 pm.