I can't see why that gsx mc would give a problem generally on another system, so should be ok.
When they are reluctant to bleed out if everything else is ok it may be worth trying another method. Pulling them out with a vacuum bleeder often gets them going or even a big syringe with rubber hose connected to the bleed valve to pull the fluid through.
Often when they get like this it's got air somewhere in the middle section brake pipe that just moves back and forth as you squeeze and release the lever.
Presume you are locking off the bleed valve before letting the lever go for another application? May just be a case of careful perseverance.