Previously I had not understood all the descriptions of wear, and elliptical holes in the winch side plate that are given in the early postings under this thread - However, towards the end of this season I investigated graunching noises that had suddenly started coming from the winch and found that the end of the axle that passes through the drum of the winch had torn through its D-shaped hole, and subsequently the axle had nearly worn through where it had been rubbing on the side plate. Having quickly replaced the winch with the old one that was sitting in the garage I got through to the end of the season. Now having the leisure to strip down the winches I understand the cause to be the drum seizing onto the axle and causing it to turn, so tearing through the D-shaped hole it sits in at one end.
It seems there is a need to get the drum axle out of the winch more frequently to re-lubricate the the axle and drum. I was fortunate that the axle of the old winch had not seized. The drum and axle seem to be just steel on steel, so will need some more frequent attention to remove rust and add lubricant. The instructions just say lubricate the winch - but a clue that the axle should be removed for servicing would have been useful! All the other bearings could be adequately done with a quick squirt of lubricant without dis-assembly, but there is no way of getting lubricant to the right place on the drum and axle without removing the axle.
Hope this can save someone else the annoying graunching noises.