crawled under the truck today and found a drop of clean fuel on the end of the positive starter cable. thinking that my fuel filter was leaking, I looked straight up to see the manual fuel filter prime pump was leaking around the bellows. The rubber bellows is hard and cracked, no surprise due to the age of the truck and it's location. should I change the whole pump assembly, or can I purchase just the bellows? how hard is it to change the whole assembly?