
It's fin bodder

I noticed a bit of dampness and paint lifting where the cylinder bolts to the casing, so have spent the last hour or so trying to take it apart. The diaphragm is perfect, but the inside of the case is damp and rusty so fluid's been getting in there. The small diaphragm that lives on a valvey thing on the top of the cylinder is hard but intact, but the inside of the valvey bit is rusty as hell, as is the plate and pin that go on top.
I can't seem to get the piston out the cylinder - Is there some knack or other to it?
And is it worth anything in this condition? It cost me £30, but buyer beware and all that. I'm just thinking of selling it on as is and either buying a brand new one, or seeing if I find anything tested and working (or sold as good with warranty) at Beaulieu next month...