Hi,
the manual states not to split the caliper, friends warned me not to do it either. But I did and luckily I had a brake caliper overhaul kit that included the piston seals and ring, plus the little "o" ring for inbetween the calipers. My 2.5NAD now has decent brakes !
Ah forgot to mention I also put the caliper halves into the dishwasher to clean out all of the Mud/fluid that was in them !