I have the magic to solve this problem. My son-in-law, that constructs swimming pools, turned me on to this when he saw how much trouble I was having unloosing these four pronged fittings. Go to a swimming pool supply store and ask for a tube of Magic Lube. It comes in 5 oz, or 1 oz tubes. It was specifically formulated for the filter covers for swimming pools to make them easy to remove and also seal them. It is a lubricant and a sealant. It is non toxic and can be used on your large water filter O-Rings as well. Basically it is a PTFE based non-melting, non-toxic, formula that is waterproof for use in wet and dry environments. A wide temperature range of 0 - 425 degrees I tried it and I am 100% sold that this is the answer. The caps and fittings come apart with no effort at all !!!!! It is distributed by Aladdin Equipment Co. Inc. Sarasota, FL 34240 and it is MADE IN THE U.S.A.