Have you checked the condition of the flexible hose to the slave cylinder?

I seek advice:
Something is worn preventing proper clutch. The engine is out. I have a new (long) activating arm and the part it fits into which was previously fitted but didnt solve the lack of clutch when the engine was in the car. Back then the arm was bent to improve leverage. This did not solve the lack of clutch as the first 'easy-fix'.
Research finds its pre-verto (original Mk2 Cooper S), yet the recommended replacement advice from a supplier is to use a Verto clutch combination. I think this involves changing the arm and the location of the slave cylinder which, for originality I want to avoid, but unsure.
The used clutch looks fine but I want to replace it while engine is out. An opinion received from one expert was the pressure plate is worn (its all original 1970 so I can accept that). But what of the diaphragm?
1. Can anyone visually inspect the diaphragm and determine if its worn or faulty?
2. Can also be advised where can I source a pre-verto clutch and pressure plate please?
3. Should I convert to a Verto type considering originality?
4. Has anyone since C-19 received goods from MiniSpares UK in a reasonable time?
Thanks in advance...

Just spent 30 mins offering comments in reply - then got logged out before posting.
Adding to kiwiwgtn's advice:
All pre-Verto parts are available from mini suppliers. e.g. Karcraft sell Borg and Beck kits (diaphragm, bearing and driven plate) for about $130. Other suppliers would be similar. There is no need to change to Verto.
The pressure plate (the heavy steel plate with 3 lugs that poke through the holes in the flywheel) usually gets scored/grooved over time and needs to be machined flat by a machine shop or clutch shop. Doesn't need replacing normally.
The diaphragm spring usually works or is cracked and doesn't work - the crack is easily seen - but worth replacing new on a rebuild anyway.
On the engine, the slave cylinder pushrod should move through about 20mm of travel to disengage the clutch.

Check out the diameter of the clutch master cylinder. Some Minis of that era came with a 0.70" plastic tank MC, these do not move enough fluid for reliable clutch disengagement if wear is present anywhere.

Fit the more common 0.750" clutch MC.

Check for wear on the actual clutch pedal clevis pin hole, clevis pin and M/C operating rod yoke where it connects to the master cylinder.
The hole in the clutch pedal wears, the clevis pin wears and the yoke on the M/C operating rod elongates.
These all contribute to too much free play at the pedal.
Compare it to the brake pedal free play.
Also there are different length M/C operating rod lengths used with the plastic tank master cylinders.
They use different length rods to position the M/C piston at the correct position in relation to the compensating port.
As the good doc says make sure it has a 0.75" bore M/C and hasn't been replaced with a 0.7" bore brake M/C.
The clutch M/C does not have a residual pressure valve like the brake M/C so this may be a clue to the wrong M/C being fitted.
A more obscure problem can be at the flywheel ridge that the diaphragm spring seats on.
From day 1 my MK1 S had clutch problems, shudder and disengagement problems.
It only took me 40 years to finally find the problem. The dealer had several attempts to fix it but no joy.
I finally noticed that the diaphragm spring wear marks where slightly off centre and then found that the ridge on the flywheel hub part had been machined incorrectly during manufacture causing the pressure plate to tilt, resulting in shudder and disengagement problems.
Hope this helps.

RonR

From day 1 my MK1 S had clutch problems, shudder and disengagement problems.
It only took me 40 years to finally find the problem. The dealer had several attempts to fix it but no joy.
I finally noticed that the diaphragm spring wear marks where slightly off centre and then found that the ridge on the flywheel hub part had been machined incorrectly during manufacture causing the pressure plate to tilt, resulting in shudder and disengagement problems.
Hope this helps.
RonR