A blockoff is the same as a blockade which is to obstruct access to something.
You'll probably leak oil. New plates are available at almost any auto parts store.
You buy a new one and bolt it on. You need to remove the blockoff plate in the door jamb to do it, as well as the license plate cover, so the inner door panel has to come off.
You dont need the blockoff kit but if you dont use one its best to remove the plastic gear that drives the oil injection unit and if your going that far you might as well spend the $15 for the tiny little plate. I am making my own block off but unless you have a mill and a chunk of aluminum this is going to be tough Check ebay. You can get the plate for $8.00