Personally I would drain the system entirely. I use a stub of rubber line, loosen the bleeder screw put the line on and drain into a clear jar. I do this for each wheel, when all are drained, I top off the resevoir and commence bleeding starting at the right rear. You will get some grungy fluid with air, that is the fluid that remains in the lower portion of the calipers, when the fluid is clear and free from air, secure the bleeder and move to the left rear. Remember to top off every third crack of the screw.
Got the message, and I'll be there.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.