Moving to Electrical...

I agree again....as I posted way back there on page one pay special attention to where the larger (aka heavier, thus more vibration) parts attach to the boards, and the large connections where the boards connect together (for the same reason).

Failure upon heating up is one of the classic signs of an annular ring crack. This type is almost invisible when the joint is cool.

When I am confronted with this type of failure I think like a solder joint. The joints fail mostly due to vibration (coupled with bad manufacturing control, but that is another topic). Some fail due to heat but these are pretty easy to spot, look for the scortching. Reflow all joints that go to cables between boards, connectors to gauges, etc. Get anything and everthing that looks like it can be shaken.

Don't lose heart. Just perservier. You are smarter than a solder joint.

So is this something I can do myself or should I take it in to a shop?
I have an old pencil soldering iron - just touch the joints till they flow - don't add any new solder?

Yes, a pencil will do ok. I don't remember any joints which would require a more powerful soldering unit. Be sure to clean the tip well, you want solder to stick to it for maximum heat transfer. I always add a little new solder to each joint, be sparing. You don't want a big glob when you are done. if you don't have any the stuff at Radio Shack is ok for this purpose.

When I did it, I didn't have my temperature controlled soldering station with me, so I had to use a cheap soldering pencil from Radio Shack, and it worked fine. It took longer than it would have, but it accomplished the task. When I reflow joints, I always use a bit of new solder. That increases the success rate. Be careful not to add so much that you solder together connections that shouldn't be.