Hey Duncan, Mikey advises you correctly. I have an 08 K12GT with that Final drive and the original spec was for 200ml, and folks were blowing out the seals. then they revised the spec to 185ml.
My K12GT FD blew out and BMW would NOT help me $$$ at all. Of course my bike WAS 4k miles and 6 months past warranty but WhatThe Heck. So I spent $3K to put in a NEW FD vs rebuild.
You’ve heard it B4, RTFM and that applies here