his stamina is due to kyubi, but its not casued simply by the chakra.....its because of kyubi's presence so to speak. the chakra doesn't need to leak out for him to have great stamina.

i mayb be wrong, but i think the 4th designed the seal not to simply contain kyubi, but to let naruto make use of its great power.....im not sure if it was mentioned in the anime, or if someone just said it on this board, but during the haku fight when the seal "brakes", what really happened was that kyubi's chakra was mixing with naruto's (same thing happened in 62.....u can c it thru the bayakugan).........

incase none of that made sense (which it probably didn't ), what im saying is, the seal is what gives naruto his stamina....he doesn't need to use kyubi's chakra himself.


as for ur other question, no he wont b AS strong without kyubi......ie: he wouldn't b able to beat neji, or last so long in a fight (like with the luck/unlucky guys). but he'd still b pretty bad ass