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In my Files here on the "OpenRC F1 F104 Tires / compatible for Differential by tahustvedt" are all 3 needed Files
If you want to use the Diff you need to print:
The difference between the Rear_Rim_F104 and the Rear_Rim_Differantial is, that the Rear_Rim_Differantial is "loose" on the wheel hub an it needs the same bearings like the front Rims.
I hope that it will help you. If you have any more troubles, feel free to ask