I had reason to remove my aluminum fuel tank a few years ago - suspected leakage. Tank tested fine - leak was found to be the fill hose. Tank was reinstalled - close to 40 years old! If I had to replace it today, I'd go aluminum.
What's the contamination? Water in the tank is often caused by a missing o-ring on the fuel fill. The o-rings get old, break, and go away (perhaps into the tank).