Do you have 671-239?

My repair manual says that 671-238 screws into 671-239, which is tapped. This is for latest models of the loco,with wheels 671-240 and 671-241. The -239 looks like a press fit into holes in the wheels that are too large to be tapped for the -238 screw.

If you have the inserts you could try various tiny screws to see if their threads are right. Or try tiny nuts on the screw's threads.

Or maybe this will find a very good parts and repair guy still in business. drtinkertrains.com

DrJolS