The quickest way to remove the belt is to cut it. The usual way is to loosen the tensioning bolts. In your picture it’s the slotted arm sticking up with a nut and bolt holding the alternator in position. Probably need to slacken the lower alternator mounting bolt too
A few months ago my ‘05 defender had no tail or brake lights. Both front side’s working and the number plate light on so i thumped the rear panel and……
Everything working again 🤪
Probably just the wheel boxes worn. Two new ones and a new cable and you should be fine. Helped my son change his a few months ago in the dark and took less than a couple of hours
Sounds like a drip somewhere as the level should only drop if the pads are getting worn and the pistons are all further out which should take longer than 3000 miles