Whether or not it drains in the back is dependent on how it was optioned. Normal foils drain in back. You can option up to sealed foils, or if it was a saltwater series, they are sealed as part of the package. If it drains in the back, you will see that the rear of the foil is simply open.
I have a 2017 with SPS. In my 3rd year we noticed leaking & gurgling similar to what you described along our port side performance foil welds. I figured I’d wait until the end of the season to get it addressed. Then a month or so later, the boat started listing slightly to port side.
I took it in at that point. We had pinprick size holes along the weld seam. Water was leaking into our sealed foils as well as port side pontoon. Got it covered under warranty. Sent to local aluminum welder via boat dealership. They took care of it in short fashion. Not sure if both were leaking initially, or if by delaying with the one, it led to the other.
However, based on our expereince, it is a quick and simple weld repair. I would recommend talking to dealer quickly to get it taken care of before summer hits. They will need to inspect and submit to Bennington for warranty approval. If approved (I would expect so with leaks and issue along weld seam), then coordinate with the boat dealership to have it repaired.