CH, the fact that the multiport handle is difficult to move only confirms my guess that the gasket is bad. The only thing that might hinder you from changing out the 'port is the plumbing connections. If you want to give it a stab yourself (and if it's neccesary), I'll walk you through it ( I do this stuff all the time as part of my job ) It would be nice to know the multiport and filter manufacturer and type. Again, if you need any help with this project, just ask and I'll get back to you, or someone else here will happily give you the help you need. - Waste