Window Leak - 2005 Sterling Europa 500

Hi All

New to this caravan lark and spotted a slight issue with our van.

Front outer window has a small leak on it's inside bottom edge.  There's a grey strip that runs around the inside that seems to have shrunk as it doesn't sit tight in the corners.  Is this likely to be the problem and is it an easy item to obtain and replace?

Other than this the van checks out 100% and after our first use (300 mile weekend trip) we're looking forward to many more.

Any help offered appreciated.