Water Ingress

I'm guessing that the topic of water ingress in vans with the sliding glass window has been covered 'somewhere' but as an unseasoned forum user Im not sure where to look.
I suspect that there are drainage ports somewhere behind the main glass panel but I cant see where, If anyone else has had this problem and found a fix i would welcome your input please! I dont really need to be spending over £1000 to get the whole unit replaced.

Thanks in anticipation . Keith

Use the 'search' box, top right, and enter 'sliding door drain' you'll get loads of results containing any one of those words,  obviously you'll have to scroll through to any that look like they might apply.