Return fuel line leak-Wishful thinking

No. You could return that fuel to the ground, and the engine wouldn't care. But if that hose has given up, your other hoses are probably in bad shape too.

 

Should be lots of info from the search block at top right. I however can not find things as they disappear.
There is a check valve in the back of the head. I posted a picture of one set up in a hole on a step. Filled it with fuel. It drained out in an hour or so. Replaced the o ring in it. Good to go. Check the check valve in the fuel pro if you have one. Injector seals can also be a problem.
Should be many posts about this to search.

 

Yes it will cause loss of prime. Supply and return fuel lines suppose to be under fuel level all the time and air tight. After gear pump in fuel system there is connection to return line with orifice to purge air bubbles back to tank. If fuel lines connections not tight fuel will flow back to the tanks. Depends how gear pump and check valve are worn it's can take hours or minutes.