I have a 6 year old Crane toilet with a Flushmate 503. I started having problems with the flush and from reading at flushmate.com figured it was the cartridge. I had replaced the duckbill insert previously and thought the top supply was OK. After replacing the cartridge it seemed OK for a week or 2 and then went back to running on. I would have to jiggle the handle and could not leave the bathroom until I knew it had stopped. There was water pooling on top of the cartridge so I figured it was bad too. Plus it was starting to "spit" from the tank bowl gasket. I was fed up and decided not to mess with this beast any more and was going to get a new toilet.
I almost bought a Kohler or AS at the local Lowes but since I could not decide there I came home to research which of the 2 was better (answer - neither). Researching a new toilet led me here and I was nearly sold on the Toto Acquia but after reading a few dozen (few hundred?) posts I started to realize that I may be able to salvage my Flushmate. I realized that I did need to replace the top supply. I had not replaced it before because I thought it would be more involved than it really was. It only took me 2 tries to get it right. (On the first try the o-ring did not seat right and it leaked). The flush is back to working as it should.
Reading here also helped me realize that when I had taken the tank off before, I had not tightened the tank evenly and that is why the tank bowl gasket had slipped. I took my time reattaching the tank this time and the spitting is gone. I am ordering a new gasket from Crane since this one looked a little ragged but it is holding for now.
So as the post title says - a very big thanks to this whole community for sharing your experiences.