Welcome nap to the Newmar forum & irv2.
Any slide on any number of 5th's or motor homes can develop a leak if the seams dry out or screws under the trim pieces come loose to allow water behind trim.
This
thread will give you some idea what can happen when let go and isn't corrected in time.
There is a
link also in thread about a 5th problem.
Hopefully you have caught it in time and just have to reseal the seam area's if not you will have some more work to correct.
Take a look at thread and you can tell us how bad it is with yours.
If its in floor area sometimes your rubber seal will have a fold in it when laying against the side wall of slide and has to be laid flat with you awning rod so water runs off and not behind the seal.