DO NOT PUSH IT IN TOO FAR !.
It only sits a couple of mm back from the drive flange. ( take note of the old ones position ).
I knocked my new one flush to the casing then tightened the drive flange onto it to drive it in square. Then I took the flange back off and put a 2mm washer I,d made in and, once again, drove the flange back on thus leaving the seal 2mm back from the flange dust seal. Whipped it back off again, took out the washer, and tightened the flange on properly.
I posted a thread on it somewhere with pics.
Del.