postmortem: i managed to return the following:- pipe wrench- rubber mallet- dead blow hammer- wheelsi am stuck with:- wheelbase ($40)- universal fit cylinder (refunded)i am using:- wheelbase ($40)- short cylinder ($30)so all told, that's a $70 repair and an extra $40 wasted, but mostly a lot of hassle and pain and grief. i can't really recommend it, but if you do, use either a pipe wrench or a removal kit to get it out of the chair seat, and make sure to get the right cylinder!