as for the key problem, you can pop the button out from behind by releasing 2 clips. you have to release the vacuum pump from the lock arm, but not entirely sure how you would do this, only done it on a MK2!
once you have the button out pop the key in the lock, then if you undo a screw or a clip on the back the lock should slide out. be carefull as there may be a ball bearing and spring behind the lock tab so dont loose them.
once the lock is out carefully remove the key then pop out the lock fingers & springs, making sure to keep them in the right order. then give the thing a damn good clean out and rebuild with a bit of silicone lube to check it all works smoothly and all the lock fingers retract properly when the key is inserted. once happy, put it back together!