Hi Dan,
Thanks for that pic and the info on the check valves and filters.
Below is a pic of the front bracket of the center section as it sits on the lower part of the housing. (I know there is a bolt missing from the bracket where it attaches to the center section

- I am sourcing that part)
What I am unsure of is how this bracket bolts to the housing. There is not enough room behind the housing to place a bolt. I am pretty sure that there is supposed to be some type of stud that slides through the bracket hole, and then the center section just gets bolted in using the two rear brackets on the rear of the center section.
Do you have a pic of the front of your BMR showing this attachment?
Thanks,
Marc