I think something similar is going on with mine. I moved it from one room to another and it became virtually unusable. Putting it back where it was makes it a lot better but it still has spells of working fine and spells of crashing. I wonder if it hasn't got a dry joint somewhere or a hairline crack in the board. Doesn't seem to be temperature related though.
Ah, now this is interesting. I picked up a non-working HDR-Fox from a charity shop last weekend and the fault may be relevant to this thread.
The box was a V1 (with the horizontal RF connectors) and the fault was the corner of the PSU PCB next to the output connector had broken broken inboard of the fixing screw taking two tracks with it. One broken track was 0V/chassis, the other was the 6.9V supply to the output connector. It's entirely possible that flexing the chassis would re-make connection.
It looked like the back edge of the PCB hadn't been fitted properly into its chassis slot on assembly, leaving it supported on one edge and one corner. It would only have needed a modest drop while upside down to break the corner off the paper PCB. The second fixing screw tab was bent upwards slightly which would seem to confirm this, and if one was assembled like this then probably there were others.
Patching the board back together was easy enough, but then I've been been doing this kind of thing for over 50 years.
In short, look for a crack at the output connector corner of the PSU PCB.
Edit: The PCB is marked 5.8V but it's not regulated. On the unit here it varies between 5.9V in standby, 6.9V when running (which is when I measured it) and as high as 7.5V when there's a lot of demand on the 12V rail, which is regulated.
