I might be able to offer 2c. I'm *99%* sure it's sealed from the engine internals,so there's no danger of it getting into the engine,but if by chance it flicks up into the cam belt when the motors running,it could get between the belt and the pulley,and make the belt jump teeth or something,so I'd say to pull the lower part of the cam belt cover off,and make sure it's the washer does no harm.Think you'll need to remove the water pump,and the crank pulley to do this...
Unless,you can loosen all the lower cover bolts,and carefully get a screwdriver or something between it and lever it off the block a bit,enough for the washer to drop out...assuming it's going to be in the right spot to do that.....hope that makes sence.