I've just replaced the OEMbrakeline for a steelflex-line. With quite a dramatic effect I must say. No more sponginess whatsoever. I've read a lot about priming and bleeding brakes (also on this great forum)and I want to share my bleedingmethod. After installing the new brakeline I filled a 60ml. syringe and a transparant tubing with oil and no air . I primed the system via the bleeder. You 'll push al the air to higher regions. A soon as the reservoir filled up nicely, I closed the bleeder. After pulling in the lever a few times, I opened the bleeder in order to flush the inevitable bubble. You simply do net get more air in the system when yoy prime this way. You let the bubble come up in the syringe, pump back a little bit of oil and close the bleeder. Topping up the resevoir and that's it. The big advantage with a closed syringe/tubingsystem is that it is a closed system and you can prime and bleed without much ado. After a night of pressure with a closed brakehandle, the system is ready to rock and roll.
Have a nice weekend y'all.