Sticking carb slide.

[Randolph Peters]

Hi Guys,
I would be grateful for your advice on a problem I am having while doing my yearly spring tune-up.
When I restarted the bike after checking valves and changing plugs, and was hooking up my carb-balancer I noticed that on blipping the throttle three carb slides were not moving.
I pulled  all the slides (carbs in place; I had totally dismantled and cleaned them less than 2000 miles ago) cleaned with lacquer thinner, replaced them and fired up.
All started moving except no. 4 carb.
I have pulled that sucker maybe 10 times cleaned, sprayed WD 40, removed WD 40 rubbed the hell out of it with lacquer thinner and still the freaker won't move. Pushing it up with a screwdriver  through the throat it slides up easily and falls back down smoothly. The resistance registers no discernible difference compared to the others.
I don't want to use any abrasive, even the finest paper since these slides are plastic.
Any advice?
Thanks
Randy from New Orleans
Ex Gpz now ZZR1200