This week, I purchased a gently used Beretta Silver Pigeon 1 12GA.
The guy I bought it from said he'd fired it exactly 110 times and I believe him.

I was removing the choke tubes (Mobilchoke system) and the bottom tube came out with no problem. The tope tube was very "slow" in coming out. I had to use the wrench to unscrew it all the way. The bottom came out with just my fingers after initial loosening. I don't see or feel any buggered up threads.
I've tried cleaning it the best way I know how and it still is stubborn. I think this is probably a simple fix but I don't want to do any further harm.

I've ordered a Beretta wrench with a thread chaser but the chaser end is brass.
Do you guys think the brass thread chaser will be enough to smooth out the threads? I'd prefer to not have to send it to a gunsmith.
What could have caused this issue? I called the seller and he said he'd never even taken the tubes out. Again, I believe him.

Along the same topic; what kind of lube/grease should I use on the choke threads/chokes?

Could the chokes be made by different companies?

I don't think its anything to loose sleep over.   Chase the threads with the thread chase and run the tube in and out a few times.

It's important to lube them.  I use whatever gun greese I have around, usually RIG, or STOS.  I dont think you need to pull them after every outing, but pull them occasionally, clean and greese.  Antisieze would probably be better than greese.  I wouldnt use oil myself.  Definitely pull them, clean and lube if you are putting it away for a while after using it.

They're all marked "PB". I don't think it's the tubes. I just think the threads might be bured.

Do you think the brass chaser will work or do I need to look for a steal one!

Did you try switching top and bottom chokes?

I think id give the factory thread chaser a chance before running a steel one through there.

Yes, it's just the top barrel that's giving me problems.