I always found it more difficult to allow the brake fluid to go all the way up to the reservior. I always take off the pad holding clips. Then the spring plate for the pads. Stick a large screwdriver between the pad and the rotor. Then open the bleed screw ( a tube and container to catch the fluid is helpful) and push the screw driver slow and steady to force the piston all the way back into the caliper. Using this method the piston will not go to far into the caliper and cause a leak to start. The pad may be damaged by the point of the screwdriver but I'm replacing them, so who cares. Once the pad has pushed the piston all the way in. I close the bleed screw. Now remember, when I do this I always bleed the system to eliminate any air and to refresh the brake fluid.
Doing this thru the caliper opening designed for installing and removing the pads means you don't have to remove the calipers.
But this method does requier a bleeding of the system.

Dave

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1970 220D, owned 1980-1990
1980 240D, owned 1990-1992
1982 300TD, owned 1992-1993
1986 300SDL, owned 1993-2004
1999 E300, owned 1999-2003
1982 300TD, 213,880mi, owned since Nov 18, 1991- Aug 4, 2010 SOLD
1988 560SL, 100,000mi, owned since 1995
1965 Mustang Fastback Mileage Unknown(My sons)
1983 240D, 176,000mi (My daughers) owned since 2004
2007 Honda Accord EX-L I4 auto, the new daily driver
1985 300D 264,000mi Son's new daily driver.(sold)
2008 Hyundai Tiberon. Daughters new car