I have a zf6 and while it is true that you can in fact remove the shifter boot from inside the cab, I dont think it's gonna give you any help in determining what your problem is.
There is a shifter lever cover on top of the tranny which you'll see with the boot removed, but I cant tell you what you'll see if you remove as I had no reason to remove it while replacing my clutch. Maybe someone else can chime in and let us know if there is any serviceable parts there.
Please keep us informed on your discoveries as I for one have 201,000 miles on mine and like to keep up on possible problems! Bill