The 9's are really east to service (I like Hayes brakes, unlike most peple who seem to hate them).
I'd suggest removing the pistons to see if they are scored from ingress of dirt etc and replace them and the piston seals if they are. The kits don't cost too much. If the pistons are in good condition lube the pistons with DOT fluid. I wouldn't put silicon grease on them as I'm not sure how the DOT fluid will affect it (for example the Stockers are famous for sticky levers and there is a special grease needed to resist the corrosive nature of the DOT fluid).
Getting the pistons out should be a doddle - remove the caliper from the mount, take the pads out and squeeze the lever. Once the pistons are mostly out, split the caliper and pull them out. Just getting the pistons to poke out will gove you enough room to lube them with DOT fluid.