The prism has no foam rot
how do you know? What condition are the door foams and the mirror bumper foam pads in? any stickiness at all, and I would get them and the mirror done. Re meter - check with a new 1.5v battery and see if the meter reading is correct with another meter. If it is, it may well have been modified inside. usually the mods are to take an SR44 silver cell and include a spacer to take up the gap for the smaller battery. The 625 isn't so good because it is an alkaline cell not a silver cell and the voltage isn't very constant as the battery ages, unlike the SR44.