transmission theory ?s

I'm looking at a side-sectional view of the transmission and differential, in my IH 'shop manual'. I can easily see how 1st through 4th gear are engaged, as they are slid forward or backwards on the splined-shaft, to engage with their respective counterparts on the countershaft. The apparently-unslideable reverse gear looks like it remains constantly meshed with a gear called the 'oiler-gear'.
My questions:
1) As the reverse-gear is on the same splined-shaft as the forward-gears, how is the reverse-rotation imparted from this gear to the bevel pinion to make the tractor go backwards? What is the gearshift lever engaging, to accomplish this?
2) What is the purpose of the oiler-gear?
3) The oiler-gear is considerably more slender than the reverse gear that drives it. Why so slender, if the oiler-gear is being used to drive the countershaft?

There is a gear called the reverse idler mounted on a short shaft off to the side of the reverse gear. The reverse idler is engaged by a shift fork with the reverse gear and first gear to effect opposite direction rotation to the countershaft. I forget which side of the case the reverse idler is mounted on. You can't see it because it is either behind the splined shaft or has been cut away in the section view you are looking at. If you can see the 2 shift forks for first/second, third/fourth you can probably see a third fork just behind the first/second fork.
That is the reverse selector fork.

Leads to one last question. My transmission makes a what? 'grinding/whining'-like noise, which quits entirely with the clutch in, is present in neutral with the clutch out, and a good bit worse in gear and under load. If the noise is there in neutral, it's probably a bearing? (As the only other thing then engaged in there is the reverse/oiler/idler gears)

Find you the newest IH you can locate; any model. Listen to it, it will have a whine.

These things use bull gears; given, sometimes they are meshed with planetarys. They are gonna whine. It is the nature of the beast.

Allan

I can live with that. The tractor moves around fine. I'll look around for an experienced ear in this area, but it's not that the transmission is giving me any problems.

Love to learn, though! Appreciate your time.