How can I troubleshoot brake issues on my Audi 80?

I recently bought a used Audi 80 and have been experiencing some issues with the brakes. Sometimes they feel spongy and other times they feel too stiff. How can I diagnose and fix these problems?

First, check the brake fluid levels. If they are low, top them off and see if that improves the performance. If not, it may indicate a leak somewhere in the system.

It could also be an issue with the brake pads or rotors. If they are worn out or damaged, they will need to be replaced.