Sadly there is very little you can do to repair the Panasonic motor. My original stopped working and I replaced it with a new motor.
Unless you can find a secondhand unit at reasonable cost, you have to weigh up if it's worth it. A new motor will cost in the region of £400
http://www.pro-cycling-golla.de/Panasonic_26V/Motoreinheit_250_Watt_NUA028R_fuer_LED-Display_artikel558d6c048ad22.html
You may be getting ready for a new battery too which will cost another £300 - £400.
I went through this about a year ago and decided that it was worth the outlay. Fortunately, I was offered a virtually new motor at a very good price, which took the sting out of the process. As you know, the PC is a great bike and since its introduction, I don't think that anything has come along which is significantly better, or maybe better full stop. In fact, many more expensive and newer bikes seem to be significantly worse and not as robust as ours. So if I was in the same situation again, I'd spend the money. You aren't going to get an equivelant bike for £800.
Before making any decisions, why not swap the motors over between your two bikes? That would eliminate the, cheaper to fix, handlebar controller as the fault.
