Where do get replacement o-ring for march pump? It is skinny silicone oring in the pump head.
Try these guys: http://www.tescopumps.com/servlet/the-MARCH-MANUFACTURING-cln-Parts/CategoriesI used them when I upgraded to the larger impeller. Edit: now that I have the part#, here's Tesco's oring: http://www.tescopumps.com/servlet/the-283/march-oring-viton-te-dsh-7r-dsh-md/Detailand of course the bigger impeller: http://www.tescopumps.com/servlet/the-226/809-815-march-pump/Detail
More beer has the O ring -- http://morebeer.com/view_product/8792/103556/Replacement_O_Ring_for_H315_pump. They also got me the larger impeller to reduce cavitation and increase flow. The bigger impellers are worth it.