Ok, small update
Thursday night I managed to pull off the pinion with the little help of a second person. Like Checkered Flag Racing suggested two screw drivers opposite to each other and a firm hold on the motor did the job. I needed a second person as I didn't have a bench vice to hold it (plus, a bench vice may scratch the nice anodizing on the motor
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Thanks a lot for your help and suggestions, I can now do the final steps in the rebuild of my TRF201's gearbox