I’d start with straight white vinegar rather than a 50/50 mix. no need to heat , Room-temperature vinegar is fine

The plastic-bag method can work for buildup on an installed spout. fill the bag with enough vinegar and secure it around the spout. A few hours should be enough to see whether the deposits soften.

If cleaning doesn’t change the leak, thats mean the diverter/spout itself becomes the more likely place to investigate or replace.

Since the new hose and washers didn’t change anything, the tub spout/diverter connection does sound like the next thing to inspect. I’d check for mineral buildup around the diverter and connection points first, and clean it carefully before replacing any parts. If it still leaks afterward, the diverter or its seal may need to be replaced.

A little extra egg yolk or a small amount of cornstarch could help give them more structure without making them tough. I’d also chill the shaped cookies before baking so the button holes hold their shape better.