You did a great job cleaning them
Glad it worked!
Some stains just never come out...someday I would love a thread that speaks to which companies have rubber that cleans easily. Definitely some do much better than others-including within the red rubber group.
I too have a stamp that some user must have used a glue on and didnt clean immediately. It is still shiny and after many cleanings it is finally only slightly tacky now. It seems to stamp ok but I havent really worked with it yet. I may try Goo gone or goof off on it just to see what happens. It isnt a rare stamp.