1963 Plymouth valiant problem!!!

What damage "can" it do?
Too many things to list.....
Get a telescoping magnet and try to find it!

Jeff

Yep, and if you got lucky it's in the pan and the magnet can get it.
Just to be clear, he dropped the screw down inside the motor while changing the condenser?
Or dropped it down inside the distributor housing?

If it went in the motor look in the oil pump gear drive slot.
You might have got REALLY lucky. :D