I had a fuel tank removed that was adjacent to my foundation. It leaked. The contaminated soil was removed and no environmental impact was created. I now have an fuel odor coming through a few of the large cracks in the interior wall. What is the best way to remedy this? Seal it from the inside? Replace the block ?

Replacing the block of an existing building is a pretty substantial task. I'd seal on the inside with a good masonary block sealer. Consider this and other similar products Sealers to protect vertical surfaces from water penetration. Great for preparing a surface for painting. Repair and prepare surfaces for painting. I doubt that you will get it 100% odor free, sounds like the clean up wasn't 100% either.