How can I REALLY clean the tracks of my shower doors??

I use hydrogen peroxide and a toothbrush

You do have a problem there Diane. The tracks have weep holes that should be allowing the water to drain. Begin by removing the doors and setting them someplace safe. Then it's just persistence. Use whatever you have to scrape the stuff out; brushes, putty knife, screwdriver, spatula, popsicle sticks. Make sure that you get everything out including those weep holes. I used car polish on my cleaned tracks. Don't know if it actually helps but seemed like the thing to do. No magic here, just hard work.

I have had good results using the Kaboom shower cleaner on mine... and a long handled dish brush.. the hand held shower helps rinse under the doors.

When I had them I used vinegar or a paste of baking soda and vinegar.

Toothbrush and Q tips and liquid cleaner.

https://www.merrymaids.com/blog/diy/cleaning-shower-door-tracks/

We redid our old bathroom and I had to take all the chrome pieces outside and clean them. My son was refinishing the shower tub in both bathrooms. I used Coke. Don't get the diet, but this is what men use for the bumpers on their cars with chrome and it works well. It is really good at removing rust spots. good luck

Forgot sorry, the pieces were chrome and some aluminum.

spray some Bleach on the tracks. waits 30 minutes.