Ah, you remind me now. Had a look at my parts book. Yes, I remember I used an ATE calliper pliers to attempt to remove these. This is a pliers with a griping surface and action to expand into a circumference. So sort of the wrong way round, if you get my drift. A disc piston normally being hollow. Thus you can grip it and rotate. The theory being that rotating slightly will break up the bond of the stuck part and allow it to withdraw. One could make such a tool out of a broken set of circlip pliers. Clearly only a certain pressure can be applied before you drive the quite soft steel into the very hole your are attempting to release it from. So its not a guaranteed method, but it is a chance.
I forgot about this part as I never had a problem getting them out. Indeed some bearing failures were the result of this 'cap' coming loose and found dangling on the driveshaft. Of course the difficulty in removal is entirely dependant on the grip, or corrosion, holding the insert in place. The Goggos I worked on where all running, or near running, cars back in the day. I had my pick as no one else was very interested. There was often excess grease around the ends of the hub carrier. I never bothered to tackle more rusty components, as I had the luxury of choice.
