Hi K55.

I think you can make narrow the situation by using voltage meter.Video data lines between UC6/7 -> UE8 were 2.05v or 2.36v when my SE/30 is showing ? icon.If there is line sticking 0v or 5v,video memory is dead,or trace is dead or touches another line.make sure have a look both UC6/7 side and UE8 side,If trace is broken,there will be difference(sounds like not this case,you patched lines...)

If all lines show you good voltage,I think UE8 is dead. 

Cheers!