Look at it this way. If you had not started it ( and seized the engine) before returning it, the owner would have had it seize on him the first time he ran it. What do you think he would have thought of you as a friend? I would be po'ed if I lent my splitter and it seized the first time I used it upon return. Fix it correctly, tell the owner what happened and you keep a friend for life.
Exactly why I checked it before we left. Done and done. While I plan on buying a splitter next year, it just wasn't in the budget this year. New saw replaced the one that died, flooding damage cost us about a grand, threw the in-laws a fancy anniversary part, bought the wife an HD camcorder so we can video our daughter, and need to replace my car this month. And so it goes. Stimulating the economy all by ourselves.