Copper pipe through cinder block wall: corrosion issue
Normally it is perfectly acceptable for copper piping to come into contact with (or even be embedded in) concrete. Pre-cast concrete block is often an exception. This is a quote from the Copper Development Assn.: 

"copper should be protected when it comes in contact with concrete mixtures that contain components high in sulfur, such as cinders and fly-ash, which can create an acid that is highly corrosive to most metals including copper"

They don't call them cinder blocks for no reason, fly ash (a residue left when coal is burned) is used in their manufacture.

Check with your local code enforcement authority, but that pipe should have been protected, both against corrosion and against abrasion due to thermal expansion. You may eventually need to cut out that section and solder a new piece in. If you can disconnect it from the tank and plug the end, fill it with water to see if there are any pinholes or leaks. Solder a new piece in if you are worried (remember to disconnect and flush first, torches and oil residue/vapor do not go well together).