Before attempting anything yourself, I would suggest seeking out a Damon dealer near you. It may even be worth a day trip to find one. Perhaps Damon issued a service bulletin if this problem was chronic. A selling dealer would be on that mailing list. And just perhaps they’ve seen this symptom previously and will know exactly where the leak is originating. It certainly doesn’t hurt to ask.
One thing you might try; saturate the enclosure in sections; only allowing the water to pour down one section at a time. This may isolate the offending portion and help pinpoint where the water is entering before exiting. My guess is that it is coming out of the enclosure at the very bottom so it probably doesn’t matter where it actually enters. I’m thinking the seal under the bottom frame is where the leak originates. If there is any “play” in that bottom frame member, perhaps it will be possible to carefully pry it up a fraction of an inch and squirt some silicone under the frame member all the way around. Again, without seeing it firsthand, it’s difficult to diagnose. A long shot is that the enclosure itself is cracked somewhere allowing the water to escape. This is unlikely unless the enclosure was installed in place while under stress. This could happen if the factory secured a cabinet up against the enclosure after the original installation. Stressing the enclosure at any time after the initial installation can cause the plastic to flex enough to break the sealant. I hope some of these suggestions will help John! Plus, our readers may have some ideas as well!