I have a new issue with the truck. It has an LT77 gearbox and last weekend it was fine. This weekend I drove the car and initially no problem to get into first, accelerate and get 2nd, but then I couldn't get 3rd (grinding noise). I stopped and then couldn't get 1st gear again (or any other). Eventually managed to get 2nd to get home and could reverse onto the drive. With the engine off I can select all gears but not with the engine running (200TDI if that matters). If I start the engine in gear then she doesn't lurch forward or back so the clutch is doing its thing, but I also can't get out of gear until I stop the engine. Any ideas???

Probably clutch not quite getting all the way to fully release. Check fluid level first.

Perfect! Low fluid level. Topped it up and bled it through and mobile again. Cheers tottot!

So... where is the fluid going ?
In a lot of cases it leaks from the slave, into the bell housing and out of the drain hole at the bottom.
It doesn't drip out, it just makes the area around the hole look damp all the time.
The slave is on the left side of the bell housing almost directly below the fuel filter.
The seals degrade and weep/leak.
Fortunately they are neither expensive nor difficult to replace.