So at this point I think most of us think that Brahms has bad posture even though he was raised in a "proper manner" he was never good at posture even if he was constantly reminded he never remembered it.
So you've found some ways to help.
Brahms tries to stand as straight as he can but always slips,and when he does all you have to do is remind him in different ways than he's been reminded before like,giving him a hickey every time he forgot,so then he can count how many times a day he's forgot about it,and change it the next day,but through the week the reminders get more intense