I think the gasket for the top of the VST was about $56.00 when I replaced mine last spring. I bought it from Don Weed & the old one was expanded also. Now if you want the injection 0-ring kit I understand around $500, highway robbery!
see this link... you will understand how easy the VST is to get apart.... My oring for the VST swelled also... that is why you need the grease... it holds the oring in place.
Oh also, the final filter twists right off... there is however a locking tab you have to release. I just blow compressed air from inside out to clean it... don't get too crazy with it cuz you could blow a hole in it.