transmission fluid filter and gasket questions , metal or not ?

People are paranoid about overfilling a trans so a lot of transmissions burn up from low fluid level. Another thing they do is let the trans warm up completely before topping it off. That burns it up too. Run it for 30 seconds in neutral and shut it off. Check (both sides) of the stick immediately. Add if necessary; repeat. Rule number ONE: If you don't know that your trans is full--SHUT OFF THE MOTOR.