Thanks guys, here it is, for future reference (thanks Dutch):
1. Remove two phillips' head screws from bottom of chair-back
2. Remove two 13 mm bolts from just above arm-rest (holding brass spacer in place)
3. Remove arm-rest.
4. Remove round plastic cover in front of big button
5. Remove leather cover, you may have to cut the inside of the leather and/or some stiching, no more than a few mm. The top of the leather cover (really the back "spine") has a plastic piece inside it that lets you remove it and put it back in place again--they most have known breakage would be a problem.
6. Remove hardware, replace broker arm.
7. Replace hardware and follow steps 5-1 backwards.
Good luck! I used fishing line to sew up my cutting, it worked pretty well w/ inside stiches and knots. Pretent you're a plastic surgeon or something, use tiny stiches and don't let them show.