aahhh...yer second sketch cleared everything for me....but I'm still waiting for leaks...
problem I see is, hydraulic cylinders are round, and you'd need to control the rotation of the tire mounting somehow, both in the stored position and while extended....However, it does look like a neat...
sorry, this has to be said....hehehehe
The used/old hydraulic ram sounds like the perfect British idea, should leak just enough oil...
(yes, I have a MGB that drips too...lol)
The drop down mount will suck if you need access to the rear and have to climb over it every time.