Minor damage to the element can be repaired without removing the rear window.
Checking work
1. Turn on the ignition and rear window defroster.
2. Place the positive voltmeter lead on the heater element closest to the power source.
3. Wrap a piece of aluminum foil around the negative voltmeter probe on the positive side of the suspected cell and slowly move the probe towards the negative side of the voltmeter. Follow the arrow of the voltmeter - when it moves from zero, there is a gap in the element in this place.
Repair
Repairs are carried out on site using a repair kit recommended specifically for this purpose, such as BMW repair kit No. 81 22 9 (or its equivalent). This kit contains a plastic conductive epoxy resin. The following are general instructions for this type of repair; if the instructions included with the repair kit differ from those listed below, follow the instructions in the kit.
1. Before repairing an element, turn it off and let it cool for a few minutes.
2. Lightly sand the surface of the element with a fine sandpaper, then clean it thoroughly.
3. Apply duct tape to the area to be repaired, leaving a gap for the epoxy to be applied.
4. Thoroughly mix the epoxy following the directions on the package.
5. Apply epoxy to the gap left in the adhesive tape, overlapping the undamaged area by approximately 20 mm on each side.
6. Allow the repaired area to dry for 24 hours before removing the tape and using the rear defroster.