Hi, thank you all, I have come to the conclusion that the seal could well be part of the problem. Question please - the skirt of the seal as supplied is much deeper than the old one ( that had turned into a 'ragged' piece of string, well that is what it looked like.) and protrudes foreword by about 3/16" from the face of the piston. It appears that this has led to a seal that has squashed and bulged outwards, or tried to, and has tightened up. Should I trim this back to be just proud of the piston face?
I will size it again.
The 'leather' is a curious, to me, grey colour and very hard. I had a spare one that I soaked in oil for a couple of weeks in an attempt to soften it and it appeared to be impervious and remained hard!!.
Gentlemen your help is much appreciated.
Geoff.