What is the best way to diagnose and fix a coolant leak in an Audi 80?

I noticed that my Audi 80 has been losing coolant and I suspect there may be a leak somewhere. How can I accurately diagnose and repair this issue?

First, do a visual inspection of the different components of the cooling system such as the radiator, hoses, and water pump. Look for any signs of leaks such as puddles of coolant or wet spots. If you can't find any visible leaks, you may need to use a pressure tester to check for any leaks in the system.