One thing that seems to escape mention in diagrams and manuals etc is the small sub-assembly that looks like some sort of idler gear that bolts on across the two crankcase halves via three 5mm Allen Head cap screws, under the clutch basket area. I believe this is just a simple little oil pump that pumps gearbox oil from the outer (clutch side) of the gearbox case and sprays the oil onto the gearbox shafts on the inside part of the gearbox, helping to keep the gears well lubricated. Even the NSR-World website incorrectly refer to this as the "Oil/Water pump drive gear". (Fourth to bottom picture here).

It just seems to me that no-one really knows what it actually does, and I would just like to know. I am pretty sure my description above is wrong too.
When I search the forum for "water oil pump idler" I get no results. This seems totally wrong. Maybe I am doing it wrong or the search is not working for some reason right now??

I discuss this more on my latest blog page here (Part 7) also if that helps?
Anyone?
_________________
[color=#808080][size=9]Yes,.. I too know how to waste Time and Money,...

I think you will find that NSR-World is correct. The water pump does indeed drive off that gear which itself is driven off that back of the clutch basket. The oil pump on the back of the gear feeds oil down the layshaft.
_________________
If I have to take the carbs off once more...

NSR-World is not correct when it refers to this as the "oil/water pump drive gear" . It is a gearbox oil pump drive gear.
If you study the pictures on the blog that I linked to, you will get a clearer understanding as to what drives the white nylon Water/Oil pump gear; that being the primary gear on the end of the crankshaft.
The gearbox oil pump appears to pump oil to the layshaft (countershaft) as you say, sucking the oil from the bottom of the gearbox through a wire mesh filter, via a pretty tricky path through the cases.
I am just too lazy to pull apart my old/parts engine to suss this out properly I guess. But still am quite curious all the same.
Surely someone on this site can easily answer this?