our mechanic of 30 years is telling us we have to replace the whole fuel pump system, yet, our oil change guy, told us we just need a fuel line patch!

Best get terminology straight, sure you can just patch it but that is just a band-aid. Your mechanic of 30 yrs has a lot more experience than that oil change guy! It would be much safer to replace the fuel lines front to back, they must be rusted and you already have a leak, or close to it. Not that expensive to do.

We were told to replace fuel pump system, 600$

What in the world does he want to replace exactly? Everything? Fuel pump, fuel lines, fuel injectors, regulator, the EVAP purge system, I would get a list of items he wants to replace and why. Then you can get a second opinion. I just do not trust oil change guys. You wouldn't think a mechanic of 30 yrs. would screw you over.

If says it needs to be replaced then I would do, TRUST HIM OR DON'T....

I find it interesting that a relationship of 30 years of business with person is questioned over $600 dollars a relatively small amount in 2016 in regards to Auto service, on a vehicle that's 15 years old. Regards

You said it brother....