is it a nut or bolt. A timing gear bolt could have backed out if not properly torqed. A nut? I just can't see getting in there. if it were dropped from the top of the motor. It would cause extensive damage and possibly seize the motor which could snap a timing chain. I know this is old but you need to pull the motor either way to check for damage. Pull the oil pan and look for copper shavings in the bottom. Turn the engine of course by hand at the crank to be sure it's free. Do a compression test. I'd do all of this before pulling the motor. The pan is a pain on these as you have to drop the exhaust and the front differential. ****** design. Also you'll have to replace the plastic timing cover along with the pan gasket. You might consider a better pan and windage tray while you have it off.