After a not-so-extensive eBay search, I have come to the conclusion that you are only one of two people that bought this regulator. The other one sold it. Consequently, it is up to you to make a service manual for this regulator and post it.
I all seriousness, I would contact
@cerich and ask him if he has a pdf of the manual or if there was even one made. If not, maybe he can point you towards the OEM and see if they have a manual. The regulator was introduced when he was still the main man for Hog. Hog-Edge still lists a service kit for these regulators, so they should have the information also. I am sorry if you tried this already.
From what I remember there was a BP-1 then a BP-2 and then the product was discounted heavily and then dropped. The only vendor still listing it is
Cave Adventurers. Others shops have sold it so they should have some idea on how to service it. Looking at the first stage it reminds me more of an Atomic or maybe a SP MK-10 Plus than a MK-25. However, it could be the cosmetics.
If you have no luck on the manual then I would post in the DIY section what the special tools are supposed to do and see what the work arounds are.