Mobile RV services usually offer an inspection for pre-purchase. However on a motor you'll want to hook it to a diagnostic scope. So will might have to take in to a shop. If you meant the block cracked I don't believe that could be predicted unless they put something in the oil to hide damage. That's what a mobile mechanic might catch. When I did mine it cost me $200, he took over 2 hours going over everything. He was very comprehensive. He did have a portable diagnostic scope, charged an additional $50 to hookup and check the engine.
