@arnoldcp Did a great write-up on how to bore out either side of the clip, leaving a small lip inside, and gluing speacers into the bored-out hole to make it wider.
Here’s my problem: I don’t have the facilities to precisely machine out the hole in the clip exactly at a 90-degree angle and to a certain depth so the spacers have a supportive lip to support them.
A few trips to Lowe’s later, and here’s what worked for me:
Play in the worm housing
The worm is not secure in its mounting. It can move parallel to the router body by a few mm, and you can “rattle” it by hand, up and down.
The top of the worm fits into a larger hole on the upper mounting. The bottom of the worm has a smaller diameter end which goes through a smaller lower hole and is secured by a C-clip on the other side. When pressed all the way down, there is ~2mm gap between the lower hole surface and the c-clip. This movement needs to be eliminated so the worm cannot slide in parallel with the router body.
Disassembly is easy - use a (preferably non-rusty) small screwdriver to pop the c-clip off. Put your free hand over the top so it doesn’t go flying, and try not to stab yourself with a rusty screwdriver.
A 12-pc bag of 5/16-inch Hillman zinc washers from Lowes is $1.28. The barcode is 0 08236 59004 3, and my receipt shows a Lowes item number of 58125.
The washers fit around the non-threaded part of the worm. Placing one washer on the top of the lower mount and installing the worm presses it between the end of the threads on the worm and the lower mount. This puts the groove that holds the c-clip about 0.25mm inside the hole of the lower mount. This is enough to still get the c-clip in, but under pressure - leaving no room for travel in the worm.