Looking at buying an IO360-A2B - it has 850hours on it. Guy selling it because he had coorsion on wings and fueselage on his airplane. Last annual was 2015, compressions 77,77,77,75. Still installed on airplane. Getting what sounds like a good deal at 11K CDN with mags, injector servo, starter, aternator. Just wondering if I should be concerned with engine coorsion and if there is any easy (inexpensive) way to check it--