In a similar position myself, here's a exploded view of the internal components:

http://www.boats.net/parts/search/Yamaha/Motorcycle/1969/AS2C/OIL PUMP/parts.html

I had to stretch out the plunger spring as it lost some of its original force and wasn't returning down.

Replace the internal seals also. They are cheap from simplybearings.co.uk, just standard shaft lip seals, sizes are 4x9x3 and 14x25x5

p.s. always take photos as you disassemble stuff, for this exact reason!

Yes that's what I thought, but the stroke should still increase at any speed if the pulley is depressed? I'm sure I gave it enough time as it went up/down a few times?
I took the pump off the engine, and a load of oil ran out of the pump where worm gear shaft goes into the pump body. Is that normal? There is a gasket there, but is that worm gear cavity supposed to be full of 2T lube?

Just copy and paste the link mate.

Yeah, my advice would be to have a shield made that would shield it from the majority of exposure. Not uncommon practice for air filters.

As said I've never had an issur and I've ridden in all sorts.from sunny to torrential rain. But perhaps your situation may be more difficult.

Some photos might be handy here so we xan visualise the problem.

Yamaha do a ruthless two stroke race bred machine called the TZ. The TZ is a full Grand Prix bike. So presumably it runs some sketchy kind of little end bearing.

http://pages.ebay.com/motors/link/?nav=item.view&id=201394504785&alt=web

That's the rods I use. Very high quality. But PJME recommend Long rods for generic builds. Mines supposively tuned.