I have the same puller mentioned. Aside from the friction of the bearing race(s) on the bb spindle alot of what is holding the motor together is are the magnet/stator being attracted to each other and the need to break that bond. Should come apart easily with the puller.
That guy on the German YouTube channel responded; between his poor English and my lack of German, the communication isn't great, but he seems to suggest that once I take it apart, the change detected in the sensors will essentially brick it without re-calibration. My mechanic gave me access to the GSD service tool which will allow me to re-calibrate it, but I'm not sure if he's indicating some sort of special manufacturer's tool or a physical process. What's especially strange is that his videos are full of GSD motors taken apart.
Wow, well really frustrated with all of GSD, HP Velotechnik and my local distributor/mechanic at this point. After a shipping delay, HPV got the 3rd motor out. To be fair, breaking the axle on the second motor was my fault/an act of the torque-wrench-miscalibration gods. However, after installing this brand new motor, the same thing is occurring as before, namely that no assistance is coming from the motor at all, at any assist level. There are no new errors, as expected given that it is a new motor. I ran motor calibration through the service tool my mechanic provided, which completed successfully but did not fix the problem. The first motor definitely failed, it was throwing out error codes left and right. So at this point we are looking at either a) HPV sent me a defective replacement motor, which would beggar belief, or b) total system failure, as, if the motor is fine, then the computer and/or wiring harness must be to blame. I can't fault HPV for service, as they have been fairly responsive for being half way across the world. My mechanic hasn't been nearly as helpful as I would have hoped especially given that I am doing most of the actual work. GSD for their part has been outright unhelpful. At this point, I can't really recommend GSD at all, despite the general feeling that they made good drive systems, and I can't recommend HPV because it's so difficult to get timely service for their trikes in the US, irrespective of the fact that GSD liquidating is not their fault and they are already sourcing new drive systems for future trikes. Any e-bike is only as good as the service you can obtain for it. Moreover, I just feel that this system, for which I paid a premium, hasn't really justified the extra cost over a cheaper solution. When it runs, it's great. But a year in, with only a year warranty - which is kind of a crap warranty - I'm dead in the water and the drive manufacturer is being liquidated. If I had known any of this in advance, I would have gone the DIY route, but I'm invested at this point.
I'm pleased to report having a little egg on my face, although I still can't recommend GSD, and only reluctantly recommend HPV to US buyers of trikes. Apparently the new motor was not providing any assistance because it was a static test - I had the rear wheel suspended with no load. This is normal - with no load, you shouldn't get any assistance. The mechanic got back to me and recommended a test ride after we came to this conclusion, and sure enough it rips again. I hadn't known this was the normal behavior, as previously the motor would kick in with the trike off the ground. My spouse speculates that perhaps this was occurring because the torque sensor on the original motor had failed, which seems likely.
I would still recommend anyone considering an assisted recumbent trike to purchase another brand than HPV, unless you have a dealer/distributor/mechanic that has the bandwidth and resources to deal with issues like this in a timely fashion. Recumbent PDX in Portand for instance is such a shop, so if you live in Portland I would recommend HPV, as they are great trikes. I happen to like working on my own bikes, but it's pretty aggravating having to put so much work into an OEM system. It's kind of the worst of all worlds - I still have to go through a shop and HPV to get parts and advice, but then I have to do all the work myself. With a fully DIY system, at least you can have the parts shipped directly to you, and there is a large community of people with knowledge of the system rather than a single company that is a black box and won't easily share information, separated from you by another degree via the manufacturer of the trike who act as a go-between.
That said, as far as OEM systems go, I can heartily recommend anything by Bosch. The Bosch CX system on our R&M, knock on wood, has been flawless, and is easily serviced at any number of local shops.
So, OEM: buy Bosch; DIY: do your research on local service options and community support.