Yesterday I discovered the near side recess in my boot was full of water. After pouring water in and around the boot gutters, I worked out the water was entering via the foam seal between the rear light cluster and the bodywork. Water had also entered the cluster itself. The connector was also badly corroded and was almost destroyed when removing. Applying clear sealant has stopped the leak (see picture) Much cleaning of corroded contacts and spraying with contact cleaner was required to get things working again. I will need to replace both the cluster and connector (if it's available separately) in the Spring