Not on a Rover, but assuming the 'wires' of the element on the glass are contactable............on my previous old car, I was able to find the (two) breaks by use of a meter, sliding the contact along until the reading dropped (sorry, was a long while ago, just remembering!). I marked the areas with felt tip pen, and then an inch either side. I then used (this was on flat glass rear screen) two old steel rules, taped them either side of the break, very close together ( seemed easier than masking tape to get a good line), and then dribbled/poked/painted conductive silver paint (specifically made for this purpose, seems to have high solids content) along the crack between the two rules. Let it dry, then checked for conductance with the meter again, and it worked. Inevitably my repairs were a little bit thicker than the original fine lines, but I don't care about stuff like that - it was a daily driver in all weathers of Scotland, so function came before form (and to be fair, you'd only notice if you went looking). On a different car I had so many breaks in the heater (perhaps someone with a sharp ring had scrubbed the interior of window, or even just demisted it a few times by hand with a ring, or a watch rubbing, doesn't take much on old cars it seems) I bought a stick on replacement, which worked well enough but never looked pretty! In that case yes, pretty much all the wires had multiple breaks - t'was ruined.
