Howard,
Not so much as the belt slipping, but have just replaced the motor with a VFD/3 phase motor combo and it was the vibration from the belt that suggested that it had stretched. I fitted the belt disengagement bar mod many years ago and found it useful. I fettled the linkage some years ago, removing most of the slop etc. and it was a vast improvement. Having looked at the belt this morning I realised that the spindle bearing and seals will be disturbed and to be honest it might be put on the very long finger. The seals never where that good and the front one always leaked, but just topped up the oil level whenever I remembered. Think I will take you suggestion and have a look at the linkage at it is now becoming very stiff.
Thanks
George