OK I took my J12 apart to lube the gasket and resize the bracelet... mine is the full ceramic but not the $500 one, as far as I can tell from the pics it is the same parts just without the extra finishing step.
Getting the bracelet out was a snap. I have no idea why it gave you trouble...
Getting it in almost cost me my hair.
NOTE THIS MIGHT JUST BE MY WATCH. We are talking half a mm of difference and all would be ok, but on mine that half mm was not where I needed it.
The reason is the tolerance on the holes for the springbar is very close to being too close to the case. This means that while pressing the end link against the case into position the spring bar sits about 1/2mm too far from the case to to go into the hole. This was a total bitch.
I say again this might just be luck of the draw because one end went in ok with some fighting, the other resisted me for a full half hour and what I Can only guess is a dangerous amount of pressure.
Finally my solution was to take the caseback off, install the hard end on just the caseback. This was easy as there was no case to get in the way.
Then installed the caseback with a little fighting, then installed the one that worked. It took fighting again but in 5 minutes I had it back in.
Let me just say I am not taking those out again unless I absolutely have to...
That's my experience so far... hope yours goes easier
BTW if it uses the same parts as mine (which I would think it does) they are just normal springbars (do you have a springbar tool? ) and actually quite nice ones at that, fat and solid and lots of "spring"