Review on 3Dman Extruder Creality Upgraded Aluminum by Alfredo Testerman

I bought 6 of these and have used 3 on my machines, I will install the other 3 maybe this week. (I have multiple machines.) Out of the 3 installed yesterday, I'm already having trouble with 2! After 3 hours of printing, I found that the pressure was only half as much. The gear on the motor was loose so the filament wouldn't push through. I made sure the screw was on the flat side of the motor shaft and tightened it very tight without pushing it to the limit. In the morning the equipment was loose again! Less than 3 hours in another print? I have the same item on other machines and they still seem to be holding up. So either I have a bad batch or the set screws on the motor gearbox are poorly machined as they keep loosening. I don't know how big the grub screw is. because I have to buy high quality ones. And I have no idea how to contact the seller to report this problem and if there is any way to solve this problem. But I am very disappointed and will not buy it again unless the problem is resolved.