No doubt it is the type that Ken has shown. And note that it is designed for a flat roof. But the Scamp roof is not flat, so Eveland's utilizes some creativity to mount the base to the roof and (IMHO) this is a possible point of failure.
Another possibility I would consider is deterioration of the vent, especially the base which is largely hidden. A crack in that would allow water in. But that should not be after only three years.
Assuming it is as Ken pictured, you can remove the four screws and then the top. Then inspect the vent base and the sealing at the roof. Its quite possible that the flat base separated from the curved roof. (The screws might be in bad shape since water sits in the holes - I even tried sticking some butyl in the holes to protect the screws).
I would think that most any vent would leak under some conditions. A pressure washer for example could force water into the openings in the vent with enough force to go up and into the base, then into the camper. The vent is designed more to stop rain from above.
Any of the rivets in the area could be a problem. They carry more weight
than most and in my Scamp at least, Evelands saw fit to use a few bolts.
Lastly, even if you do stop all leaks
from the roof, water will likely get in through the side (intake) vent at times. If the wind and rain (or hose spray) hits it the right way I doubt there is any way to prevent a leak. If its just once in a great while, then mop it up and get it dried out and it should be OK.
And I assume they did not do anything to restrict air flow when they added the weather stripping. That could reduce the effectiveness of the fridge