How To Maintain Hair Clippers by Stripping and Cleaning - see my pinned comment

He didn't lubricate the internal parts - and he did not apply the proper lubricants too them - i.e. the right grease on the motor shaft pin and coupling.

And having a low pressure, compressed air supply of about 30 PSI is better at cleaning out shit from devices.... is better than a hair dryer.

Other than that it's a pretty good video.