N 14 accessory drive seal

[the missing link]

looking for a n 14 guy....
Dads done the seal on the accessory drive a few times .
I have done it once myself .
It does not take long before its leaking again.
Its a 525 plus .
Is there anyway the shaft can have play in it .
At my wits end with it .
I have checked the shaft for wear , the cover for cracks . I have replaced the speedy sleeve.
Just wondering what else could be causing this
Any info is much appreciated.