Grammatically, it would be:
"If Walter loses Stamina, he loses an additional Stamina."
Also, his leg crippling should probably state that he is -1 Speed until the end of the turn.
But really it seems that the Pendulum has swung back too far. He gets unlimited uses of Marksman, which is interesting, but quite often not that important. Truly, you're probably better off just giving him that and deleting all the war wounds. As long as he doesn't have the Ambush bonus of +4 dice on virtually all combats for no reason, he seems pretty balanced. He can scale his Fight and Will up to 5 if need be, he has a decent Focus, and he can reroll his combat checks. Not bad. With a few clues under his belt, he can do vaguely alright against a Color From Outer Space.
-Frank