ok, so i found out how to get the black cage off - had to use fine penknife blade to unclip the side retainers.
that went ok on this first one. but i'm going to have to watch that vid again, because i'm having no joy pinching
the white button mechanism. not coming out at all :-( ... will report back on progress... do not want to screw this up, most of these work reasonably well, so i don't want to end up with worse than before !