Jason,
Its a 2000 KDX 200, in Wisconsin (below 1000 ft I think)
I can not find any signs of a bad seal, so I did just what you said, took the carb apart and cleaned it. No sign of anything major, a few specs in the float bowl, but that's it. I switched needles again, went back to the stock 1174 (mid clip)versus the 1173 (2nd from top) bumped the main up to 155 (from 152), pilot is a 45.
I know this sounds backwards, but the 152 ran great in the summer at 80 to 90 degrees, plug looked just a tad rich at the time, I figure with the temps around 60 its time for an adjustment. No plug chop today (not enough room), I'll just have to fly by the seat of my pants, as usual. I really hope the plug fouling was due to bad gas... Will find out Sunday as I am running a HS in Illinois with a new batch of fuel. I will carry my fanny pack and a few plugs...just in case.