If you have bought a cheap and cheerful silver slave cylinder they have no seal spreader in them.
So unless you drive it nearly every day it will suck air in past its seal.
To fix this, either pinch the one out of your old cylinder (if fitted) or contact me, I made some a while ago and have a few left.
The manufacturer of these cylinders was contacted by a supplier here and didn't care.
AP cylinders do have the spreader, if still sold.
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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.
