OK, it's an easy fix. Start thinking who the lucky nonprofit will be.

Look at the third photo with the ground face up. Note the worn or dull area at the notch of the lower jaw. In order for these to cut effectively the ground faces must come all the way to the edge ao they pass each other with zero clearance. Here's how to grind as good as new.

1- do not grind the flat face, under any circumstances. Be very careful, if you damage the ground face it'll be extremely difficult to fix, and require special tools.

2- you need a bench grinder with a stone that still has a sharp corner. If you don't have one you need dress the stone to make a sharp corner.

3- with the grinder off, set the tool rest so you can put the into the corner above the wheels centerline. You want to be high enough that you'll be grinding to a roughly 80° angle. You might need to be creative in arrange the tool rest to give you the right angle.

4- Grind, with the flat face up, plunging the notch directly into the corner (no back and forth motion). Warning, it'll get hot fast so do short bursts, and either quench in cold water, or rest between grinding sessions.

5- Grind until you've gone past the worn zone, so you have a sharp corner at the peak of the V and 2-3mm up each side.

6- repeat same process on other side, be careful you want to match both sides so the 2 apexes of the notches pass each other.

7- reassemble the cutter, and do not cut spokes with it.

BTW- wear real safety goggles with a single lens across the bridge of your nose, and close fitting sides, especially when dressing the wheel. Particles come off the wheel at 7200 feet per minute (roughly 80mph) and can bounce off your nose or cheek into your eyes.

If you don't have access to what's needed, PM me and you can send me the tool and I'll grind it for you and return it. No charge for charity work.