Pictures

I'm guessing you need the right size brush to fit in that crevice, maybe a toothbrush would work. That plus Softscrub with Bleach spread in there with a bit of water. Let the Softscrub sit in there for a full 5 minutes to give it time to work.

Years ago I used an aluminum cleaner. It dissolves the top layer off somehow and makes the tracks sparkle. Look for it.

In the first picture it almost looks like a caulking job gone bad.... Could be a build up of calcium and or lime deposits. I'd try some Lime-A-Way, just squirt it on liberally and you'll see foaming action right away, let it foam for a while then scrub with a brush and repeat.

For calcium stains use white vinegar & water in a spray bottle 50/50 works great, I clean a lot with the vinegar & water mixture. You could also try that in the tracks if the other (great advice) the members gave you. Let us know what works for you, and yes the tracks are gross.