I wrote this in reply to someones similar problem.
The filter is sealed by a rubber 'O' ring and for the lack of or the wrong type of lubricant, it jambs solid.
Best way I have found to get it unscrewed is with a standard pair of pliers, however used the wrong way round!. Put the plier handles into the corners of the filter and use a bar or screwdriver though the end you normally grip with for leverage. This forces the plier handles into the corners where the plastic is at it's strongest and unlikely to break.
The best lubricant I have found to be silicone grease, the worsted type is 'Vaseline' which swells the rubber seal and jambs the filter solid.
Cracks around the threads of the housing are normally caused by either the 'O' ring swelling, over tightening, or frost during winter.
It should seal, (thinking as if a clock), with the 'bar across the middle of the filter', pointing at twenty to two.
I might add, I fitted a new housing to a customers van one Saturday afternoon, by Sunday lunchtime the unit had cracked in the six O'Clock position. Now I am sure I did not get it wrong, my only doubt is whether the customer had a 'play' with his key spanner after I had left. The customer had bought the unit locally and on asking the dealer he told me Trauma's advise as to why it had cracked was we had not 'opened' the filter???. I am not even going to explain this only to say as a reason, it's complete rubbish. What it will mean to you however is you are not getting a free replacement, even if as I believe it is faulty plastic and or manufacture.