Hi John,
Some of the tangs on the friction plates were a little rounded on the leading corners of the tangs. I overcame this by simply rotating the plates through 180 degrees when reassembled the clutch so that the damaged corners were not taking the same impact and, what had previously been the undamaged following corners of the tangs, are now forming the leading edge. I hope that this makes sense (basically, I just put the friction plates back on the other way round).
I don't know if this is an acceptable solution or not, but it appears to be working so far....
Simon