Well, today i've tested the Kyosho diff ball like Fraz said
in here. To experiment other options i used the 10.000 diff oil like Q'on said in the
nanotrax forum.
Sanded the rings with 1200 sandpaper, lube it with 20wt shock oil and...OMG, this thing fly over the RCP track. It's true that i had also changed my 6t broken pinion but the diference btw the stock diff and this one is amaizing.
Then i tried with 10.000 diff oil. It's ticker, perhaps the motor don't like it so much but i think my car had better velocity with it. Perhaps the first battery wasn't so charged as this one, but when ir reach the final strait the car was literaly flying over the RCP track.
One big problem - dirt. If with the stock diff there were always problems with the dirt and so on, now with ball diff the problem, at least for me, was exponencial. Any tiny hair is a big problem for the dnano's diff.
Other problem that i had, before the kyosho ball diff installed, was the 6t pinion. Only last 12 to 15 packs. The gear mesh was normal, as indicated in the manual. Don't know if it was the crashes, the constant braking or whatever. Thank god i have another Porsche 911 GT3 for pieces...
Thanks Fraz and Q'on for your help.
Nuno