Weird
I had a slight leak once from the standard filter on my Evo and switched to K&N. I've had three since then with no problems.
So was the oil pressure switch in your earlier post
http://www.ukmonster.co.uk/monster/s...235#post562235
actually faulty too or was the oil leak just down to the loose filter?
The genuine K&N filters should have holes in the hex head for lockwiring so maybe worth taking advantage of that feature for future peace of mind.