This has to have happened to more people than me. But I had to work out a fix on my own. Many drawers on cabinets or dressers have some plastic parts that in the end are taking all of the stress of holding the drawer runner system together.

What happens when they break?

You aren't going to be able to get a replacement part. So either live with a droopy drawer forever. Or invent a solution. Here's the solution I invented.

This particular drawer had a metal runner running through the broken plastic part and then another metal runner. Take 2 blocks of wood, either find or cut the right size to give you the correct depth. Take some fender washers, you don't have to grind one edge flat, but seems to work a little better if you do. In this case, I probably could have ground them down further and been better final fit. But this will do. If you don't have a bench grinder, do the best you can with whole washers. In this case, since there's a metal runner that goes between 2 parts of the broken piece, I used 2 fender washers on each side, and a spacer washer between them. Drill some pilot holes in the right place to get your side to side spacing, and use short wide threaded screws to attach. In this case, I had to cut away a part of the runner to make it work.

I've never seen anyone describe how to fix this problem, so just thought I'd pass it along, just in case it would help someone else.

https://imgur.com/a/uWfB9Hd