As already stated it doesn't matter so long as it's mixed to the right ratio. Read the container.
Fuel filter- if there's a shutoff on the fuel bowl, shut it off before removing the filter. Then turn it on after installing the new one.
What tech did you speak to that told you the full synthetic oils aren't full synthetic oils?!:confused2::shocked:
And, for discussion sake, say he's correct, what real difference do you think you'd see on a 2004 diesel engine on a small tractor between 'true' full synthetic, and 'fake' full synthetic? ANY synthetic is going to be better than the dino oil run in it since 2004. And it's not like you're going to run it in pro drag racing or the Indy 500 anyway, right?
Furthermore, and after spending several hours researching synthetic oils and their ilk, it's not quite as simple as 'natural' foods or 'organic' produce but here is the wiki dictionary def on synthetic oils; (and unless you're running a turbine powered jet engine, 'fake' synthetics should do fine for your diesel tractor, IMHO). I've run Amsoil, Mobil 1, and Rotella T6 in my tractors with absolutely NO issues whatsoever. When I had my foreign auto shop we sold exclusively Castrol 5w-30 oil, in the days before synthetic was commonplace, (except Amsoil), from 55 gallon barrels I bought in bulk.
FWIW,
http://en.wikipedia.org/wiki/Synthetic_oil
BTW, Redline 5w-40 is not a diesel specific specked oil, their 15w-40 diesel oil is. Don't know if that matters to you but at $12/qt you must like buying expensive oil.:confused3:
I used to also sell Redline's Diesel fuel catalyst for all my diesel Benz and other customers. At the time it was the only product Benz approved/endorsed for their engines. It helped thaw out many frozen fuel lines/filters....