I tried searching a bit, but this seems to be a rather odd problem....
I just bought a used mountain bike with 9 spd Deore LX components. The shifting was a little funny, I lubbed it up, but I am still having trouble getting the rear derailer to shift the full range of the rear cogs. Ive played a bit with the limit screws and adjustments, and the cables seem to be decent enough. Does anyone have any ideas what the problem might be? The derailler also doesnt look bent and the cassette isnt worn very much. The only thing I know to try is lubbing the shifters like I lube the brifters on my road bike, but I dont know where to squirt the oil on mountain bike type shifters.
You start the rear derailer adjustment with the chain on the smallest cog, unless you have one of those new, wierd, backwards derailers. Assuming you don't have one of those, put your shifter in the first position, back off your cable tension and adjust your stop so the chain is on the smallest cog. Increase cable tension until one click of the shifter takes the chain to the next cog. Do your final adjustment of the stop screws and that should do it. If it doesn't, replace your cables and housings and try again. That's what I'd do. If that didn't work I'd suspect shifter problems. I wouldn't expect to fix them by squirting oil in them.
Well I took apart the shifter, and discovered one of the pieces of the ratchet mechanism was frozen in place. (Bassically the downshift lever would only push on the white piece of plastic, and its little hook thing would never engage the gears -- if that makes sense :-) ). Oiled that piece up, and the thing works like a charm!
And actually, I've had quite a bit of success oiling brifters --- my rx100's on my previous road bike needed it about once a month.