You are a later version as mine is a 14k number. I have tried wire pulling gel and water. Water works for about 6-8 shots and then is evaporated out. Both leave a powder/carbon mess insdie the can and on baffles.I hear using wire pulling gel does even better than water. Have you tried anything other than water?
I'm not sure when mine was made but the Ser. # is 16514... If that means anything. It was a new, old stock item.
BTW, 10ga shotgun brushes help with the 22lr can cleaning the tubes. Centerfire stays somewhat clean; however, 22lr is a nasty round and expect to pick out a lot of melted lead on stuff.