I am usless at DIY, but after changing the rear wiper blade on my E53, and then WD40'ing the spring in the arm, I was still left with a patch at the top of the arc that the rear wiper did not clean.
So I bit the bullet and ordered the 3 BMW parts I needed to replace my rear wiper with the E70 version.
Five minutes at lunch and it was done, sorted, and it works the actual 'reach' is slightly smaller, but its a full arc.
E30 320i
E36 325i Coupe
E46 330i SE
Now an E53 4.6iS