It won't hurt the seal, unless the circlip is out and the outer part of the bore is corroded.
The clutch lever arm, if worn that much will make the slave cylinder piston hit the circlip, this will limit clutch travel.
3 ways to avoid this (apart from the best, a NEW arm):
1. Remove the circlip, it serves no purpose once the cylinder is on the car.
or,
2. weld a bit of rod onto the pushrod to lengthen it 20mm.
or,
3. Heat and bend the top of the arm, towards the cylinder.

I do reckon your clutch arm is well past it, I throw them away when worn 1/2 that much.

_________________
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.

Thanks Doc.

I wonder ... if the SC piston hits the circlip (as a result of over lever over travel) will this break the seal in the SC and let a bit of air in ?

I have a new lever arm on the way, so I will install it and see how it goes.

_________________
-- Simon // VMCI Member 2674 --

Seals let air in on the pedal upstroke, when they are old and tired or poor quality.
It's the seal, not the piston that is the problem. Telltale clue is getting a bit of air on every pedal stroke when bleeding.
Any brake shop will sell you a seal, they are a standard 7/8" cup type, no hole in.

_________________
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.