Unfortunately I'm sure the box has to come out. The clips have to be taken off a certain way to prevent chipping or cracking of the housing. I made this mistake, and found that finding a good used original box is very difficult and expensive. Usually the boxes have been broken by previous owners trying to service them, or the drain hole nipple is broken or the mounting tabs are broken or cracked. This is something you want to be careful with. If you don't care about originality the aftermarket boxes are actually decent enough. But like Kilgon said, the back clips will be very hard to access. Good luck!!