Diesel losing prime with small leak

Hello, so it's been one thing after another with this truck, starter, fuel issues, bellhousing exploding, glow plugs...fuel issues again. But for right now I cannot for the life of me figure out where my small prime leak may be, I'm pretty sure it's in the engine bay at LEAST (i've replaced or checked lines, tank switch, sending units ect). it doesn't matter what temperature it is but it takes about 8 to 12 seconds of starter before it will run and after the first start it starts immediately all day long and runs great, no smoke coughing or anything until it sits overnight. One of my questions is where are all of the olive seals?

I figured I may ask on here before I pull the last of my hair out

Things that I know are good or have been replaced: Glow plugs, Tank switch, Fuel Pump, Return Fuel system, and the olive seals from filter to IP

I would check the glow plugs again and only use Motorcraft or Beru, I believe is the manufacturer.

And check the glow plug system, the connecter block for the glow plugs will get burned up.

This sounds to me like some glow plugs aren't getting warm for start.

Edit: And I always used the block heater on a heavy duty appliance timer when cold, much better starts.