I know this is an old thread, but in case other new owner are like us--looking through all the posts--I'll share what I've learned. Wrote to Dexter axle with our serial number: "we find no such number in our records." Contacted Grand Design and the head of Consumer Relations told me "we only put self-adjusting brakes on these trailers, so you don't need to be concerned about this." Given what I had read in this Thread, I thought I should check further, so I crawled under the trailer and discovered we have Lippert brakes. Called Lippert (by FAR, the most helpful of all the places I spoke with) and learned that I indeed have manual adjusting brakes. I was send a description on how to adjust them and then a manual on the brakes. I called GD back and expressed concern that they are giving out incorrect info and they responded "sometimes we switch products in a production cycle..."
This does not give me hope that the company is in touch with the people building the trailers.

Dick Durst
2021 Imagine XLS 22MLE
2019 Ford F-150 Lariat