Is the plastic piece on the outside of the hood, meaning accessible with hte top lifted? If so, that is called a Rolleigrid, I believe. It was an add-on piece Rollei sold. It can be removed- pull back/down on the center tab at the back of the hood and pry it up from the back edge.
Short of a Maxwell, an Oleson screen is a great improvement. For $30 or so, hard to go wrong. If you want better, the $200 Maxwell will be waiting
EDIT: I was writing while Gerry M was posting his comments, so sorry for the repetition!