The most recent "bench bleed" method does not use the fittings and tubes to recirculate the fluid- - - -just use plastic plugs to stop off the outlet(s), clamp the MC in a vise, and gently move the piston about 1/4" or so repeatedly until the bubbles stop coming up into the reservoir. I can't imagine how a master cylinder could be damaged by doing that. It's just purging the air that's trapped ahead of the piston without actually circulating any fluid.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!