Yes, You'll want marine speakers that are weather proof. You can try what Arkhillbilly suggests and contact the dealer to try to replace just the bad one , or replace the pair with something else.
Did you check for a loose connection? It could just be a speaker wire.
If you decide to upgrade and replace with something a bit better, JBL makes some decent all weather speakers that should mount right where the current ones are mounted. Amazon has a pretty good price on them.
JBL offers many choices for outdoor marine/rv applications
Check out the JBL website.