My cover port broke off very early. I never bothered to replace it and have not had any problems. I think it does help with water proofing but I never take mine into standing water and get out of the rain as soon as possible.
I have seen some people make a cheep replacement by cutting off just the end of a power cord and inserting it in the space. Of course you must take it out and replace it with an intact power cord when you want to charge.