In my experience everything is a little beefier in the 999.
I am not sure what year, but the sprag changed from a 10 element to a 12 element. The low/reverse drums are interchangeable, but some 999 drums have a ring around the area where you are catching your fingernail. That's how I know it is just the end of the machining. The band does not ride there. It would be very unusual for the reverse drum and reverse band to be worn because in normal driving they are hardly ever used and it is not a shifting band.
I sent you a link about the black trans fluid. It explains that those trans with the overdrive, burn up the overdrive clutches and turn the fluid black.
