I had this issue on my drivers side glass last month.
The glass would wobble when driving. Took a look when stopped and ended up pulling the glass out. The sealant sheet had failed from the bottom to pretty much the top of the glass. Only a small bead was fixed at the top. I was careful as the plastic guides in the adjustment motors are fragile, so don't pull the glass to much! I learnt this with my last car. The passenger side seems solid, so I'm not fiddling with it until the reflection looks drunk.
Read of many fixes that all worked. In the end I settled on silicon high temp sealant. Halfrauds had it for £5. Reason for silicon was that it apparently allows heat to dissipate from the heating element (not sure if foam pads do this as effectively but plenty of people have used them without reported issues) and that araldite etc. are permanent ( which was the point surely!) but I read it's easier to remove the glass if it is knocked and broken with silicon, but impossible with proper glue. Who knows if that's the case, as most breakages prob mean the whole glass and backing plastic assembly would need changing.
In any case, getting the glue/ pads or silicon even all across the glass, like the OE glue, is handy to get the heat into the glass. I used a egg box lid and elastic bands to put a bit of pressure on when drying, looked dodgy, but it dried in place.
I've had the silicon seal for a couple of months now, with plenty of rain and bumpy roads. We'll see how the expansion coefficients react to frost...
