Brakes - Only 1 Channel will bleed

[Muskrat]

History:
I just finished a brake overhaul including reman'd caliper's all around, stainless brake lines, and an ABS delete.

Problem:
I went to bleed the brakes today and can only get one channel to bleed (LH FR and RH RR). When depressing the brake I can hear a metallic "ring"

Only thing I can think of is bad seals in one of the MC pistons. Anything else that might cause this? I don't think anything got clogged.

I guess my options are rebuild the MC, or buy a new/reman. Any suggestions on this? Rock Auto has a variety of vender's, any suggestions?

 

[Barnes]

Was the master cylinder drained during any point of your ABS delete/brake work?

 

[Muskrat]

Yeah, the whole system was drained. I don't see how it could have been avoided.