The problem is familiar, one of my two units is also very tight.
It’s worth trying with rubber gloves.
If it still doesn’t work, then wrap the lower, thinner part with cloth and grip it with pliers. When taking it apart, I always remove the Pyrex glass first, so it doesn’t shatter while I’m forcing it.
The rubber gloves have always helped me, but it’s still tight, even though I lubricated the O-ring.
I also had trouble with another tank. There, they also suggested a solution: putting it in the freezer for 20-30 minutes and then trying it.
Unfortunately, this did not help in my case.
Thank you very much for the good advice! 
With a similar method, with the help of a cloth and a vise, I managed to take it apart! A very good flavor-producing atomizer, but I don’t think this is normal. Even if not for other reasons, I suspect it won’t be my favorite atomizer!
Yes, it’s an annoying problem, I struggle with it sometimes too.
I always plan to replace the O-ring, hoping it will be better, but I’ve been too lazy so far 
If I don’t forget, I’ll do it next time I build and write if it helped or not!
Hi!! If one of my radiators was leaking/loose, I cut 2 strips from a bicycle inner tube and used them to seal/grip it. This always worked for me!!
So the ultimate solution: buy one or two Dwarves, then you won’t have such
This is completely true in this form!!
I think this will be the key to the solution…