Wondering if anybody can help?

Car was driving fine (78 van), pulled into the servo to get some fuel.
Started the engine and couldn't get it into gear with the clutch pressed in of course.
Will go into gear if the engine is not running, then I can start it and drive.
Have checked the clutch fluid all ok, does this sound like the slave cylinder or something?

Slave cylinder could be sucking air around the seal.
Original slave cylinders had a shaped plastic bit behind the seal to maintain its shape. The silver aftermarket ones don't.
So if replacing seals in the latter, pinch the plastic bit out of an original cylinder and fit that in there.
The seal is a plain 7/8" cup seal, available from almost any brake shop.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I took the spring off and appears to be working fine now.

But now the car is running rough as guts (separate issue)
Will book it into the mechanic tomorrow