To replace the catch, is far far more effort than replacing the whole quarterlight. I'd forgotten about the aftermarket catches, which is the alternative option.
ps -i moved your question out of 'other' section into technical section.
Rays correct they are quite difficult to do and are a form of rivet and you often find its not just the rivet thats worn but the whole catch, and as for getting some original catches they are rarely on ebay as new old stock items, and go for silly money for what they are.
Cheers
Kevin
Lovejoy 1968 Smoke Grey Traveller (gone to a new home after13 years)
The easiest optionis to replace the quarterlight for one with the catch intact. These turn up on ebay now and then I paid £10 for the last one I changed.
I think I'd go for the aftermarket one now -probably more secure than the original