oil pump

your oil isnt going to drain out but there would be a hole left in the clutch cover (on the inside_ and dirt and water and other crap could get inside your motor. better to get the kit to make sure it does not happen or just leave the gear in there. what is it hurting?
 
yes, you'll have to add oil because you'll have to take the clutch cover off. the easiest thing to do is to just drain the oil and then take the cover off