I also use vinegar. It resides in the tub after use as well and keeps everything from smelling bad.

Fabric softener eventually goops our top loader up. After a few years I have to remove the agitator to manually clean the gel. Cutting it with water beforehand helps and I suspect using a Downy ball would help even more.

If that doesn't work, try a cup of lemon juice. That always works well for me to break up sludge.

I use TSP to clean out the washer grime that builds up. On the front loader in Washington, I would throw two cups in and run it on the hottest (sanitize) setting. I would usually pour a gallon or so of hot water down the soap dispenser to get more water in the drum. (It was a self watering front loader so if there were no clothes, it would almost be dry).
That cleaned the soap deposits really well.

The nice thing about vinegar is it won’t hurt your clothes if it’s not all rinsed out. It will dissolve soap scum as it’s acidic. It also kills mold spores. Store stuff is only about 3% acid so you can use a bunch without a problem.