I sent you an email.
Here's what it said, for the benefit of others:
The kind you have is not easily repaired.
Terry recommends the Korky 528MP MaxPerformance fill valve, which is essentially-identical to the Toto TSU99A.X Universal Fill Valve which Korky makes for Toto. You can get the 528MP at Lowe's (they call it a 528MPK on Lowe's web site). It will work in any Toto. I have it in several of my Totos and it's easy to install and adjust. Down the line if you had the same symptom that you now have, all the working guts of the valve are on a little quarter-sized cap which you can just replace in 30 seconds for like $5.
Here's the valve: http://www.lowes.com/pd_336988-868-5...3284948&rpp=32
Other stores have it as well. Caveat: There are other Korky 528 fill valves (plain ol' 528 with the white cap, one with a red cap, and a 528T with a blue cap). You don't want them. You want the 528MP with the silver cap, because that one will be adjusted to the proper refill ratio (the amount of water that refills your bowl). If you don't use that one, you won't start with your bowl properly filled; it won't have refilled to the right level before the tank refill shuts off.
There's a video on how to install the 528MP here: http://www.youtube.com/watch?v=Gw7HvHtaA84
Good luck and come back with any more questions.