Here are a couple of suggestions. Caution the parts are made out of brass and then chrome plated so there somewhat fragile and soft.
Put two nuts on inside the housing locking them together and allow as much room as possible between the nuts and housing. Turn the inter-most nut to loosen the threaded bolt.
Put the nut back on without the o-ring and see if you can get it locked on to the threaded bolt and use that to turn it out. You may want to put a small washer in the nut to take up some space between the nut and bolt head.
Put a odd ball nut inside that will not properly thread on to the bolt and try to turn the threaded bolt out.
Once you get the threaded bolt loose it should turn freely.