Heh heh heh - Oil also does one major other thing - lubricate! I usually change my oil by look, feel, and smell. If you do not do short trips that never warm it up (that puts acids in the oil that never boil out) then usually the first thing that makes it need to change is that it would be "saturated" with soot. You can easily tell if it is by smearring a little on you finger and looking at the edge of it, and in the ridges of your skin - if it is clean and 'clear' , ie, no soot, than it is still fine. The soot will settle out in to the valleys of your skin on your finger, and if the rest is clean your oil is fine. Diesel engines need oil that disperses soot - something gas engines do not make as much so do not need as much. Also, this is exactly why mileage-based changes are not the best, but more for people who need a 'schedule' or they will forget. There are so many variables that come to the oil's sooting that are different - like a lot of idleing, especially when cold, will make you need to change your oil way quicker, but you are putting zero miles on it, so you are in essence 'not doing anything to it'
As to which brand of oil - that makes no difference. What matters is the rating. The attitives. That is what is keeping the engines going. The reason early engines never made it past 100K was because the oil attitives, not the oil, were not as good. One of the best prices is super-tech 15-40 diesel oil at Walmart that comes in 2 gallon containers. That is if you would give walmart business. And of course there are other oils that have even more additives in it, making it even better. Kindof funny seeing people fighting for these oils and regular oils are will wear your engine out quicker, and then watch them drive away, petal to the metal with the engine cold... heh heh
As to synthetic - the only main advantage it provides is stability under thermal variablitie - ie - wide viscosity range. If you do not need that, then you do not need a synth.
Just my . 02
As for the ATF as an injecter lube, I just go to yellowstone fumeroll's from time to time and throw in a little sulfur. Just kiddin - that sulfur is horible - yeah good lube, but when cold idle w/ wet cyl walls, gets in oil, and turns into a nasty nasty acid H2S04 - sulfuric acid - that is what is in your BATTERY! Think about THAT when you complain about no sulfur!