[Al Fielder]

In another post, I described how to remove the pinion from the Bosch motor. It really wasn't difficult. Taking a Dremel to remove the pinion seems to be alot of work, with risk, when a puller will work just fine. The press fit for a new gear should be in the .0003-.0005 range, specially if you are installing a gear with a P.D. of around .7-.8 so that you don't yield the new gear.
If the new gear yields, you lose the press.