I have a '07 1.8 vvt, i have noticed a leak from the oil filter cap, which is a clear greasy fluid (oddly enough)

I have replaced the oil filter but not the O ring seal, (old one was in good condition, one with new filter was wrong) the cap is on tight enough and does not come loose after driving but the leak is still carrying on.

The only thing i could think of would be the expansion rate of the plastic cap being higher than the metal filter housing? might be wrong.

Not sure what steps to take next, any help would be appreciated.

Thanx Tim.