It's quite common to see points gaps self-adjusting with the later Lucas steel-backplate cb assembly because the method of attachment of the fixed point carrier leaves much to be desired. But not so common I think for the heel to be worn down the way BSA 500 describes. (I infer that the problems recounted here relate to these later versions.)
Replica points kits for the steel backplate units have been of very variable quality and some just aren't fit for purpose: flimsy construction, serious mis-alignment of the contacts when fitted on a decent Lucas backplate, loose contacts, dodgy rivet holding the bent tin opening point carrier to the heel - all and more of what TT said.
I'm not sure what the quality is like of any of the bits that are available from the usual sources to be honest.
Ideally I'd always use an earlier brass backplate if one is to be had. Although they suffer over time from worn pivot posts and oval holes in the heel, these weaknesses can be sorted, and if needs be better contacts can be grafted onto damaged or worn parts. The heels on these parts last pretty well - a bit of lube (as also says TT) is good, using the felt strip and pimple supplied.
It is also worth bearing in mind that it is possible to fit a BTH or Bosch contact breaker unit of the correct rotation. It may (depending on the individual version) require suppression and recreation of the integral keyway/ register on the male taper to get the internal timing right (or repositioning the camring), but the design of these cb units is superior to the Lucas one in my view.
As an aside, the temptation to regard these things as 'fit and forget' has to be resisted, a bit at least!
The general advice back in the day, per any number of Owners' Manuals, was that a mag should be sent to a 'Lucas service agent' every 10,000 miles for a complete strip and replacement of any worn or defective parts, with interim maintenance such as points cleaning, lube and re-gapping every 3000 miles. I'd say these days, for the miles most folk do, that annual removal and checks to the cb unit and HT pick-ups and brushes is probably enough. Simple checks can be revealing, especially in relation to oil ingress, excess armature float or wobble etc etc and are often the stitch in time that saves nine.
