Jack Sim (not Sims, Sim), who has restored over 300 Model 90 series ECOs says again, the only way is to drill it out. Be carful, the threads of the retainer are not at the top of the retainer, they are about 3/8" down. Start by drilling a small hole down the center of the retainer, keep enlarging your drill bit, as soon as you see the edges of the threads discontinue drillings, it is time to chisel out the remains of the retainer.
Keep in mind, after restoring over 300 of these units I should have come up with a better way, but consider this retainer has been in this unit for over 50 years, I have never found a better way.
I still have a few NOS retainers available.
Last edited by Jack Sim; Wed Apr 16 2014 11:19 PM.
Author, 1st & 2nd editions of Gas Pump ID book, 3rd edition is now available at www.gaspumpbible.com
Air Meter ID book also available