Fluidmaster problem - getting the cap off

Please respond ASAP - I won't have Internet access after 40 minutes!
My model is black with a white cap.
The toilet won't stop running unless I lift the arm on the Fluidmaster, after which it seems to be fine.
So I checked out the instructions for that online, and it said:
Problem: Debris is lodged under the valve's seal. Debris may consist of calcium deposits, minute pieces of corroded pipe, rocks, rubber, solder, etc. that are carried by the water stream to the seal area, where they become trapped. Some well systems without a filter constantly circulate debris.
Solution: Shut off the water supply and remove the valve top (Model 400A: lift arm first). Cover the opening with an inverted cup, and turn water on and off a few times. This should flush and remove water line debris. Turn top assembly over and clean seal surface by rinsing under water. Replace top (400A: lift arm first) by rotating clockwise.
(end)
Nice, except that when I tried it, I couldn't get the cap off (yes, I twisted counterclockwise). Prying didn't do a thing either. I'm afraid I'll break it if I put any more pressure. What am I doing wrong?
Granted, another possible solution was listed here, which I'll try in a few hours:
http://www.fluidmaster.com/html/troubleshooting.html#q5
Problem: The water level is set too high and reaches the top of the overflow pipe upon shut-off. This results in small amounts of water pouring into the overflow pipe, causing the valve to turn on to refill the tank.
Solution: Reset tank water to a lower level by using the water level adjustment clip (see illustration) located on the link of the valve. Squeeze the two sides of the metal clip together, then slide clip down the rod.
Again, please help ASAP - the plumbers are inspecting the building tomorrow and I'd rather do it myself. Thanks.
Lenona.
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Twist it 1/4 turn counter clockwise. Sometimes you have to push down on the top while turning.

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What I've done in the past to save time and aggravation is simply buy a new Fluidmaster valve, but only replace the top piece of the old valve. There is no need to replace the entire assembly which requires draing the toilet , disconnecting supply line, and risking leaks. It seems like a lot to spend money on a new valve to just replace the top part of it, but to me its faster and easier than changing the whole thing.
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On May 28, 4:04 pm, snipped-for-privacy@yahoo.com wrote:

You have to PUSH down (hard) and turn counter-clockwise at the same time.
The post will try to turn as you do. Grasp the post with your right hand and use the palm of your left hand to push down and turn.
Seems like you need three hands but it can be done.
If necessary, HD sells the replacement seal. Usually just a cleaning works.
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