We have a 5.5 hp Briggs Intek with pacer pump, recently Dad was complainin about the thing takin way longer to fill the sprayer.  After playing with it a little, it appeared to be pumping alot of air with the water, so I figured it was leaking in around the seal.  Couple weeks later I found the time to take it apart, and ordered a seal for it.  Soon as I had it apart, Dad said it had started working fine again, but went ahead and put the new seal in anyway.  These guys have parts if you need anything:

 http://www.dultmeier.com/products/0.901.1557/1159