If you are asking about steel VS plastic, I don't feel that would be the issue. I have tried a few motors in the last few years. Not by choice. I went through probably 3 personally and have all of the off brands screw up within a very short time. The last few brand name motors have been flawless. I don't know if they are plastic or steel but the brand name have worked through 40 C below and up to 40C above.
The distributor that was specified has brand name products. My experience has been that they stand behind their products. DMS good - Skywalker -bad
Sonicview 360 Elite,Viewsat Ultra,Coolsat 5000&6000,76cm Radar Sat Dish and SG2100 Motor