I just moved into a home that has an older oil tank. When I took a peak underneath I saw a fair amount of rust on the bottom of the tank. No leaks yet, but I am concerned. The tank is 3/4 full and is literally built into the wall behind three painted sheet rock walls. I would like to hold off until I use the oil this winter if I can, but have to admit I know very little about home heating oil and oil tanks. Thanks.