You could try an isopropyl alcohol soaked cleaner, inserted, hopefully all the way into the bowl.
Then, use an eye-dropper to put some more alcohol in the bowl. perhaps the cleaner will wick it up into the aluminum tube area.
The thing to avoid is alcohol seeping out between the tenon and stem, that ruin the finish, so you'd have to proceed carefully.
I seriously doubt the sticking stem is because of the aluminum tube, but the alcohol would also free up the stem.
As long as no alcohol is on the finish, you won't do the bowl any harm.