would get caliper onto a bench,make sure piston seal is located into groove in caliper and outer dust cover is also in its groove,apply plenty of brake grease,make sure it is proper brake grease,to seal and piston,the trick is to get the outer dust cover over piston without pulling it out of its groove,once the piston is past the dust cover it holds it into the groove and apply equal pressure to piston and push it all the way in,good luck
wickham
June 2010