Ok got a new one to go on...a mercedes bosch one I bought on ebay...now getting the old one off what is the best method....I read its a no no to put a big alan key in the recess in the top, but that seems to be the only way to turn it. Apart from that brace the pump assembly....and turn ignition to on and pound the brake pedal until it goes hard....

 

Just recently did mine. I wedged it tightly in place, then used a hex bit & ratchet wrench. One hellish grunt later & it was off. Alternate is to use a strap wrench. Screwed on new one, a GM equivalent replacement from the bay & tightened with strap wrench due to no hex on top. Problem instantly solved! (delayed braking due to failed accumulator.) Now I can drive it anywhere, anytime!

 

chickened out got the shop to do it. Mercedes bosch one...smaller but works a treat car stops now.