New Zealand Datsun Club

If changing out your hydraulic cylinders fixed the clutch not going into gear problem, and it worked fine before that. And now it's slipping, odds are your clutch is poo'd.
They aren't too dear if you have the right hookups. Is this car your only means of transport? You need to hook it up in the air, and remove the gearbox again. Then pull the clutch off. you should be able to tell pretty much straight away if it's worn out or not.
It's also be practise to have the flywheel re-faced at the same time. Which means removing it from the engine.
Most places will do a flywheel grind for free when you buy a clutch kit.
I can get you a really good price on a new clutch kit if you like?

Bartman wrote: It's also MANDATORY to have the flywheel re-faced at the same time. Which means removing it from the engine.
Most places will do a flywheel grind for free when you buy a clutch kit.
I can get you a really good price on a new clutch kit if you like?

Clutch systems do the flywheel machining as part of the price of a new clutch, and they're pretty cheap too.

I'd still be looking at the thrust bearing collar and the clutch pressure plate height too if I were you - my 510 seemed fine, except when I changed the clutch I noticed huge indents in the thrust bearing from it always being hard against the pressure plate "fingers" (which were also worn), and if you've had a similar issue it could cause premature clutch wear.

If you do need a new collar they're quite common and it's not hard to removed the old one and press the new one on if you have a vice.

Does your clutch fork have any play at all? If it has no play at all, you have a problem.

A kit comes with a new release bearing anyway, So if a carrier change is required, no biggie.
John has a point about checking the free board at the fork, and seeing if the fork can be moved fore a little.