I just purchased a 2005 Pete 379 with a c15 acert. It will not start without a little ether. After some research I read that a common problem was the check valve in the filter head. I’ve replaced both check valves twice with no luck. You can hand prime the pump and you can hear the fuel returning to the tank and it never gets stiff. You can also crank on it and hear it returning into the tank. I have put a fuel gauge on it and I’m only getting 10-15 while it’s cranking over.