are you speaking of the small rubber boot cover?? I when to superior nissan (la puente, ca) they were $3 each. I picked up 6 since i don't know when they will be discontinued. and like you said it stinks when it leaks. the shifter kit that replaces the top cover includes a gasket i think. or some liquid gasket would work best. i would assume you replaced the trans mount already. have you checked to see if it has torn at all?? I know the 'drift' oriented companies offer all sort of bushing upgrades. such as RS-R makes a complete bushing kit that i believe is harder then the energy suspension kit.

www.phase2motortrends.com send them an e-mail or call them. they would be able to help you out with more questions on the shifter.