[electrowizard]

saand you rock my friend!

Yes I know how hard it is for me to diagnose hovering over the circuit, it is even harder when just being described on a forum. I'm doing my best though!

I think your idea of a poor ground connection floating Vgs too high could be bang-on. My soldering iron is not capable of heating anything attached to the buss bars, so the driver ground to the source lead was only clipped on and may have slipped loose. The oscilloscope ground lead is grounded through the mains, which shares a common ground with my 12V gate driver. And the oscilloscope ground lead was more securely fastened than the gate driver.
The battery was not being charged, so no ground loop there.
However, I just remembered.. my TVS is permanently soldered between source and gate. Shouldn't that prevent the gate from breaking down regardless of the actual potential of the source lead? Hmm..

I decided on a last minute trip to the cottage for several days with family, so I will disappear for about 5 days. I'll try and digest the problem while I'm away and come back at it full-force.

And yes, my propane-torch soldering skills have improved dramatically. I can replace a mosfet in about 45 mins now... the copper bars take almost 10 mins apiece to heat up and longer to cool down. I know that kind of exceeds the recommended soldering profile... I wonder how much damage I am doing to them. Hmm.