Jen,

I'm really glad that you have good news regarding the spraying! Maybe Jim will continue to improve if you keep the fosters separated from the "main herd" - I know it's not ideal, but a recuring theme in all the threads regarding fosters is that the first priority must be the health and welfare of the existing cats!

I don;t know what else to suggest - although it would be a real pity to be in a situation where you have to rehome Jim - I suppose adult cats are much more difficult to home that cutsey kittens!