I agree, and to add that this department is safety-critical because some of the wiring is unprotected i.e. a short to the airframe and you probably have a fire. Only wires downstream of circuit breakers (or fuses) are protected from a short circuit.
Anyway, it is a great excuse to knock up a new CB panel, with nice custom engraved labels 
The panel will be rewired and upgraded from American O&N to German standard. ;-) Takes 1-2 weeks and will be performed by Airplus @ Friedrichshafen.
Thanks for all your comments!
That's a very good decision! Just be careful... there's many different "German Standards" too :-))
Yeah but looks promising. I made a typo above, it will take 1-2 days, not weeks...
It seems you have decided a radical and probably more long term solution.
However, diagnosis of this kind of thing is greatly aided by one of these
They told me to check the current draw on the thick lines. My maintenance shop did it and it was 7 resp 10 amp with air conditioner on (they were suspection the a/c). So it actually can't be an overload.
What you actually want to measure is the DC resistance of that line, it looks like a bad (high resistance) joint. 7 amps through one ohm is 49 watts of heat, 3 ohms produces 147 Watts etc.
Have you ever seen a UK 13 Amp mains plug burn up when the fuse holder oxidizes and produces a few ohms resistance!
The panel is in the plane since it's conversion in 1998. It should survive until Nov 4th, hopefully. But I won't fly across the Atlantic which I do plan for the next year. So this needs to be solved.
