That is great!
Don't mean to be the Devil's advacate It is just the Airplane Mechanic in me are you sure the clip was not in or could it be in the bottom end or did it go out the exhaust?
I am sure you split the case to inspect for it and cleaned the exhaust chamber to look for it so you know it won't show up later on top of piston like emu67's engine.
Sorry to be a a**whole or bearer of bad news but I sure would have checked, that is just me thhough as a indycar mechanic years back and airplane mechanic we can't leave missing parts to chance, must tear down , inspect , and exhaust all possibilities.