[Mr Gazza]

Hope someone can help me out here... I'm stuck!

I have a very early coffin type brake master, 13mm for single disc (It is possible that it isn't originally from a Monster).

I have a brand new Brembo seal kit and all the components that I can compare seem identical and correct for the master I have.

Here's the problem. I was expecting to see a circlip with holes for circlip pliers, but this is not the case. I see a retaining ring in the bore with no visible means of removing it.
There is a new ring in the kit which looks dimensionally identical to the one trapped in the bore, but no clues as to how it would be removed, there is no break in the ring. There is a shallow external annular groove which could potentially engage on a wire clip, but that would be an impossibility really?

Instinct tells me that it should be knocked out from behind, but the only access to that would be the tiny 2mm? hole in the banjo end of the master. it would have to be knocked out with an O-ring and plastic ring. I don't think they would transmit any knock!

Any clues please? Am I in need of a special tool or a special person to do it for me..?
Looking like a precise tubular drift to push it back in again too, with the rubber boot in place.