Today i crashed pretty severely into some thick mud and managed to pack my dura ace nine speed rear sti with mud, how should i go about cleaning/repairing this without compromising the function of the lever?

take a new can of wd 40 or something(new because the pressure is as high as possible)with the red plastic tube(pressure is even higher when all the oil has to flow through this thin tube). then take the plastic cap away(the one you take away when changing shifting cables)and spray into the lever. if that doesn't help, the lever is ready for the trash can. i had this several times and couldn't repair the levers because you can't change something inside(springs or so) or take the lever apart just for cleaning.
that was one of the reasons i switched to campagnolo last year, because the shifting mechanism is isolated way better.

you can allso use teflonspray (I like it more)

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Tarmac SL2
Epic 2009

If it is ready for the trash can, you may as well bathe it in hot water, power wash it, vacuum it and anything else you can think of to get the mud washed through. Then use lots of teflon spray to re-coat the insides and expell the water.

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http://worksrider.wordpress.com/

I would:

1. Remove it from the frame.
2. Use pressurized water to remove all the gunk (not too liberally).
3. Dry it with compressed air
4. Use prolink to lube all the joints, pivots, etc.

You can take the lever+shifting mechanism off the body, this will make it a bit easier to clean and make sure there isn't any sand left when you are done. If you tried shifting too much after you fel chances are your shifter is damaged, the sad thing is that you have to replace the whole shifting unit (if you can find a deal on a whole new shifter this might even be cheaper, I think the replacement part costs about 120 euro, but don't quote me on that)
Try cleaning it as good as you can, an airgun wil help a lot (high pressure air) . Remember to regrease everything when you are done!
Hope you get it to work properly again, exactly what happened to you is why I don't like shimano handles for a cross bike. The way they work makes them real dirt eaters, and no small parts can be replaced to make it work again relatively cheap. (as you can guess I switched to campagnolo, but I still think the shimano levers shift a bit better when your bike is really dirty. You can apply more force when you shift up because of the bigger lever. I also like the shifting cable sticking out the side, it helps you not to slide over the levers when they are wet and slippery. This shouldn't be a problem when you race, but if you only ride for fun you can't switch to a clean bike every 3 km )

Ummm, Yeah so i tried hosing the lever out, and then i let it soak in a solvent tank, and then i sprayed the internals with a silicon lub. No luck, the lever is trashed, thanks for the advice though.