Yep, it's a very common repair for these, the gears don't get greased and the worm eats the bronze gear. I just fixed a couple of these a few weeks ago, and I have another one on my bench with the same issue.
Pretty sure Henning's has those gears in stock. Depending on the vintage, you may have to work a little to get the old gear out, the new gear sets have a set screw, so they drop right in. Some of the older ones were pressed on, so you had to do a little discrete hammering to remove it, making sure to support the motor frame so you didn't wreck it. Of course, if you have a press, then do it the right way, that's how I take them out.