Two independent studies rated Opti-Lube XPD as the best diesel fuel additive.
One of the best diesel injector cleaners available is Fleetguard's Asphaltene Conditioner. The cleaner is a premium fuel additive and is made by Cummins.
It has low sulfur, use additive
Biodiesel is an additive or alternative to conventional diesel fuel.
Mix it with the fuel, usually just put it in the fuel tank just before filling up with fuel
You may be able to find a diesel additive and just use the gas in the tank.
No. Fuel tank needs to be dropped and entire fuel system flushed.
There is no fuel additive that will increase mileage. This is a myth. None of the snake oil additives work.
It is not a great idea, you will be likely to ruin your fuel system. Jet fuel is low lubricity compared to diesel fuel. Perhaps someone can identify a commerially available lubricity additive. The US military has a lubricity additive to make jet fuel acceptable for ground vehicle use.
none, use a good fuel additive and change filters regulary you will have no problems.
If it was just exposed not run for a while just replacing the fuel filter draning the carb or fuel injectiors, and running a gas additive in your fuel for a bit so it will break down any diesel that is left
JP8 was invented to be compatible with diesel. You don't really need to put any additives in it, but if you insist I'd use something like Howes Meaner Power Cleaner.
New fuel filter. Clean EGR valve and clean intercooler and pipes. Add injector cleaner to fuel and also fuel enhancer additive.