Before you do that (or is it too late?), you should remove the seal while you have everything apart and clean out the groove it lives in. Crud builds up behind the seal and keeps the piston from retracting all the way during normal use.
diddo...
you can use a 90 degree pic, but be careful. you dont want to score the groove either... good time to make sure piston and bore are smooth like a baby's butt.
I actually took apart the front brake solely for this reason. I got a front tire put on yesterday, and the guy that did it for me, pointed out that it was rubbing and was prob because the piston was sticking.
So the front is done, and I went to tackle the back, just going to bleed it and put some new fluid in it. Then I had trouble finding the bleeder valve. When looking at my book its pointing to a spot, where on my bike, is a screw.
I think the PO lost the bleeder valve, and replaced it with a screw.....