grab yourself a magic marker and get ready to tear it apart, you can see the brand name on the one I use in the photos below

take that end cap off using needlenose, pops right off, no loose ink floating around but be careful still

there's the innards

pull the "cigar" out of the inside

pull the tip off and use a paper towel to wipe the insides out. throw it all in the plastic bag and put it in the trash
go to OSH or hardware store, buy a 1/4-20 screw with the largest head you can find (the round head screw is too small to hold the o-rings on, need to do some more work here EDIT: see new info below)

buy some 012 o-rings and install on the screw. they roll up without problem and the both the 6 and 7" senkos fit the o-ring and the tube
I've got an order of 1,000 o-rings coming in so if you want/need some orings let me know. think my price works out to about .03 per, so its that plus USPS for however many you want, not looking to make a living off of selling o-rings but I can't see using 1000 in my lifetime so I need to get rid of some.