So I opened the motor today, and yeah it looks very bad. the gears are completly destroyed.
Yes, those are toast. They look like the typical white nylon gears. Depending on the actual material, they might not be as tough as the material the GMAC gears are made from. But if there were any remnants of the missing / damaged pins or anything else still in the motor from the previous issue, even a tiny piece of metal, etc, it could have chewed up *any* gears (even metal ones).
The GMAC gears in your original pictures look like they are still usable, other than the missing / damaged pins securing the assembly together. So you could ride with those until they fail if you need to, once any bits of those pins that could still come out are removed to prevent damage.
as mentioned before, the last pictures were from the last problem were the cables were completly chewed up and resoldered together. then the gears (the blue ones) were exchanged for an older part laying around (the black ones).
I don't see any black gears in this thread's images. There are only the GMAC blue ones in the earlier posts, and in this post I'm replying to there are white gears (albeit quite dirty with contaminated grease).
So I do not know what motor they came from and if they were actually suitable for this gmac.
when fixing the cables they were soldered together and insulated with heat shrinking tubes.
then the cable coming out of the motor was mainly taped together. unfortunetly I dont have clear pictures of how that was done.
if the images in this latest post are of the present state of that cable, and it's not new damage, I highly recommend pulling the undamaged part of the cable on the outside of the motor up and thru the axle until entirely undamaged cable is inside the motor. Then cut away the whole length between the motor internal connections and this new undamaged cable area, and strip back the undamaged cable jacket inside the motor enough to secure the new wiring to where the old wiring used to go.
this removes the entire damaged and spliced area, which then removes the risk of destroying your controller again, as long as the axle is correctly mounted to the bike such that the wiring is not stressed and the wiring is then secured out of the way of anything that can damage it.
It does shorten your wiring by several inches, and some setups may require moving the controller closer to the motor to accomodate this, or using an extension cable between motor and controller. If neither is an option, then I'd recommend getting a new motor-side cable from ebikes.ca to completley replace the existing one, that will be long enough to fit all the way from the internal connection points to wherever you need the connector to be.
If it *is* new damage, I think you should carefully look at how the motor is mounted and the cable is routed, as something could be repeatedly damaging it again there.
If the cable is rubbing against any sharp edges, either the edges need to be rounded off, or the cable needs to be rerouted, etc.
So there was often a slight chewing or stuttering (after the first repair) specially when starting the motor and not allready driving.
according to my friend this should not have been a problem, but I think this also contributed to destroying the motor.
If it was running sensorless, some "stuttering" is normal if you are not pedalling first to get started at least a tiny bit and then going, depending on the specific controller setup and the actual load the system has to get moving and the conditions it has to do that under.
(my trike is so heavy especially with cargo that sensorless doesn't really work very well on it regardless of controller type or brand).
Replacing the whole hall PCB is probably the easiest way to fix the sensors, but you can get individuals as noted previously and just solder them in.
If not, the next steps would be to clean everything out and install new gears.
Gear assembly for GMAC Motors
how to I get the gear part out? I was not able to loosen or take out the gears.
AFAICR, it's just held in by the key fit in the slot shared with the axle, so a "gear puller" centered on the axle end and jaws on the metal triangle should be able to remove it. There may be a snap ring before you can do that, but I don't remember from when I had mine apart, and I can't tell in your images. But you can verify that with Grin before ordering the assembly. (I think there is also a thread here somewhere with info about this, but I don't have a link).
This video by Grin probably shows the procedure, but I haven't watched it, so you'll have to verify that.
endless-sphere.com
they may work, but you won't know till they're actually working in there...and if they aren't working as needed they may pass a static bench test but fail to work as needed while the motor is running for various reasons. 
