Front brake caliper piston cylinder bore question?

[canada karl]

On the earlier 530i brake caliper(the one with the 3 bleed screws)........does each piston cylinder bore have a large port at the bottom of the bore and a smaller port across from it? It's hard to tell when the caliper is not separated into two halves. Some bores look like they have a smaller port but some bores appear to either not have one or they are plugged...kind of a black carbon dot. Are these some sort of brake fluid return port? How in the world can they be cleaned out if indeed they are plugged? Or is the caliper kaput if those small ports are plugged?