Last time I went out on the bike, I couldn't get low gear on the motor. I'm pretty sure that the problem is the clutch. I tried to open the motor to have a look, but I couldn't get it dismantled; I'm going to get a special tool that might help with this. Meanwhile ...
I contacted Panda. They sell various ebike kits, including a Xiongda dual speed motor kit (they call it a double speed motor, but that's a misnomer) for £225. That's a pretty good price. If you buy direct from the Chinese supplier Xiongda, you'll get a better price, but that's eaten up by the carriage costs, plus the motor isn't laced into a rim, so you'll need to buy a rim and spokes, lace it up and then balance and true it, and that, when I did it, took me many hours. The Panda rim looks good; it's a double-walled rim, that makes it stronger.
I paid them Monday evening, they dispatched the kit on Tuesday and it arrived Wednesday morning. I put my usual thick inner tube, gel insert and Kevlar tire on the wheel, and used it to replace the old wheel. I used the old controller, display, throttle and motor gear change switch, so it was very little work to do. Half an hour later, the bike was ready to roll, so I took it out on a couple of tests. One is a speed test on a fairly level road, the other is a hill climbing test nearby, and it works fine. Tomorrow, I'm taking it to Hastings for a day's caching.
I've also contacted Xiongda. I'm planning to buy a replacement motor from them, plus the tool for opening up the old motor. The new motor, will be built into the old wheel, and if I can fix the old motor, that might mean that I wind up with three working dual speed motors. I think they'll let me choose how the motor windings are done - there's a tradeoff here, you can get more speed with less torque, or more torque with less speed. Because of the way I use this bike, speed isn't important, but more torque would be very good.