I changed all the brake hoses (new). My master cyl. showed signs of leaking so I changed that as well (had one laying around). I bled the pass. rear, perfect. I bled the driver side rear, perfect. I tried to bleed the pass. front and it spurted out a bit of air and fluid and after that initial spit, nothing further. Same thing with the driver's side.
Are my caliper's stuck in a position where they do not let fluid to go thru, or do I have another issue?
I tested my master cyl. before I put it in by placing the reservoir and pouring some fluid in and when I pumped fluid squirted out of every orifice with great force, so I guess the mast. cyl. is fine.

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1976 280C
SLOWER DRIVERS KEEP TO THE RIGHT.
DRIVE RIGHT PASS LEFT

One thought would be that you lucked out and got loose junk stuck in both front bleed screws.

The system is split diagonally so if it comes out a rear caliper, it should come out the opposite front corner unless there is a proportioning valve somewhere. If there is a proportioning valve (I don't think you have one), it could be stuck or need to be "reset" by pumping the pedal a few times with all bleed screws closed.

Michael

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Usta haves '69 250/8, '76 280C, 1971 250C 114.023, 1976 450SEL 116.033
Current have, 1983 300SD 126.120

Replace the bleed valve or simply R&R to clean it and the orifice of debris if you cannot locate a new valve. I suspect you simply stirred up the crud and it needs to flush out thoroughly. But, keep in mind that the crud may be a sign the caliper is badly rusted and verging on failure if it has not failed already.