I have always used a common old C-clamp to push the piston back into the caliper assembly. It seems to work quite well.

I have never done a brake job on a Mercedes, though. Will a c-clamp work, or should I be on the lookout for the thing that looks like a scissors-jack?

What do you call it, by the way?

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Semibodacious Transmogrifications a Specialty

1990 300D 2.5 Turbo sedan 171K (Rudolf)
1985 300D Turbo TD Wagon 219K (Remuda)

"Time flies like and arrow, yet fruit flies like a banana"
---Marx (Groucho)