Mikeainia
You have covered most of the problem areas but two more sometimes raise their heads.

The Handle it's self shorts the control lines together and the second is the model shorts the lines together.

At the Handle a cable as in a Hot Rock handle shorts the lines together. Or the electrical connnector for the lines is mounted on a piece of metal that is electrically connected to the other side of the handle.

At the model the problems can be the wires inside the model are tight together and the Cya glue softened the insulation allowing the wires to short. This mayshow up asan intermittant problem. The bellcrank is metal shorting the lines together. A remedy for thisis to place an Egg Insulator in one of the leadouts inside the wing.

As for the loss of signal through the lines, a typical set of .015 lines will measure about85 ohms each at 60 foot length. Larger size flying lines willhave less resistance. I have a 91 ohm resistor in series with each side of the output and return connections on my test board to simulate this line loss during testing.

I use 3/32 (Minature) ear phone jacks and plugs for my connections. I then make a Test Cable with a phone plug on each end to test the system without unrolling my lines. If it works with the Test Cable then I unroll my lines and connect them up. Now any problems are only associated with the line connections. The Test Cable is also handy when working on engine running problems or engine warm up ortune up. The Test Cable is handy when adjusting the servos in the model for other functions.
Clancy