[PMCBR]

This is a “for what it is worth” thought.  The track that holds the slide seal leaves a little space between it and the skin of the coach.  Water can collect there and migrate inside.  This may be the cause..   later models started using a horizontal slit in the skin of the coach in that area to direct water away.  Maybe someone with a later model could display the slit.

Thanks Gordon these are exactly the suggestions I am searching. I will check the seal for water seepage, along with the seam at top of slide out. Any other suggested trouble spots to check are greatly appreciated from all.