I did my 87GT up with a full set of prothane black bushings. Whoever claimed they were impregnated with graphite was full of crap. Anyways I bought an extra 15oz tub of energy suspension poly grease to make 100% sure I'd have no squeaking. I lobbed as much as I could on and packed it as much as I could.
Less than 300 miles later, one of my front arms started squeaking

. Apparently even if you have zerk fittings the pressure from the grease gun can eventually destroy the best bushings. Rubber for me from now on, much more durable and maintenance free even though its more trouble to install.