Don't know if big diesels have intake air heaters. Those are used mostly on small diesel engines (tractors) that don't have glow plugs.
And yes, you can buy starting fluid for diesels.
Anyway, OP has clear symptoms of loosing prime. Lot of diesels do have glass, or clear tubing allowing for fuel flow observation.
Do you have such? If not, I would try if I can add one.
Diesel fuel lines operate mostly of vacuum, so you will never see fuel outside, but on some design topping off tank, or parking on slope where tank is higher than engine will build enough pressure to see wet area following morning.