I'm guessing we're talking about different setups. There is a shaft that runs up through the filter which has a white plastic sleeve which is about 1/2" in diameter. It is much bigger than the center hole in the filter. That sleeve rides on a spring that goes through the filter and into the nether regions of the ps pump. There is a small nut which is threaded onto the shaft that holds the sleeve and spring in place. This sleeve/spring is what places upward pressure on the reservoir lid. To put the lid on, you have to press down so that the cap nut will thread onto the shaft and enable the lid to seal to the reservoir. Does this make sense?
Essentially, there is no way to simply lift out the filter without removing the sleeve...and the entire shaft turns when I attempt to remove the nut holding the sleeve/spring in place.
Maybe I'm overlooking something obvious.