Well maybe it's too late for this information to be useful but after having so many troubles with mirror caps, currently I use another method to remove the mirror caps without disassembling anything in the mirror. I insert a plastic sharp tool between the base of the mirror cap and the mirror body at the indicator ligth side (not so easy, as it's not supposed to exist a space to insert a tool there) then shift the cap toward the front of the car. Repeat that along the edge of the indicator light. That releases the tabs that connect the lower part of the cap to the indicator. By doing this, the upper clips are released almost automatically. Spares me a lot of time (or maybe I'm very lucky).