Fiamma toilet

I had a problem or two with my Fiamma toilet when I first got my van, which I have now sorted. I now have a new problem.

I've never seen a Fiamma cassette toilet before and sincerely hope I never see one again. For anyone who doesn't know, the cassette is larger and flatter than the Thetford one. To flush, there is a handle at the front to open the valve, and a knob to flush the fresh water, then push the handle back in to close. Underneath, in the cassette compartment, there is a big red handle which is pushed to the right to lock the cassette in position and then pulled to the left to release the seal to get the cassette out. This is tricky sometimes, too, because the big "pin" that the front handle's connected to doesn't always push in far enough and also the handle seems to slip off the thing it connects to underneath.

What appears to be happening is that the red handle is moving to the left (i.e. backwards in the van) while in use and/or the handle at the front is not closing the seal properly. The consequence is that the whole thing is leaking into the compartment. This has happened to me twice over the last couple of weeks and, because the door to take the cassette out is inside the van, what's been leaking has been leaking out of the compartment and onto the carpet. The red handle is currently jammed into position with a piece of pipe lagging (the things you carry in your van, eh? ) and when I empty the cassette and put it back, I have to make absolutely sure the handle in the front is pushed in hard. 

Sorry this all sounds a bit garbled, unless you've seen one and know what I'm talking about.

I just got home yesterday and am going to try to soften up the rubber seal a bit and try to loosen the handle which opens it. I know the toilet hasn't been used for several years as the previous owner just used the shower compartment for storage.

Nora