02 power steering leaking

My 2002 windstar power steering pump is leaking at the pulley shaft seal.
Do I need to buy a new power steering pump?
How hard & long does it take to change the PS pump?
Is this a common problem or could I buy a used pump from a auto wrecker?
Thanks

Rockauto has them for your 2002....
Cardone rebuilt for $47.79
Cardone new for $134.79

IF it is not leaking to bady I would try some LUCAS power steering conditoner ( not sure if that is the correct name) Have heard numerous positive comments from people that used it. Worth a try.