This is my opinion only. That torx bolt that BD-X uses is not intended to be taken out for the once a yr maintenance, its more like a one time use only (install). It is a self tapping bolt and rips the threads out when you pull the bolts out.
Stock junk torx bolt.
I agree.
They are Triangular shanked thread-forming screws. Reusing these screws are the cause of thread damage in the case.
I recommend replacing with a stardard M6 x 1.0 button head capscrew.
Should be able to pick them up at an auto parts store or someplace like Fastenal (or you can order online)
Length may vary, I used 16mm on my dad's 07 Z1