It's possible that the central tubes on your cartos are collapsing. Take a look through the central tube on the carto: if you can't see daylight, then your tube has collapsed.
You might want to try this trick. Straighten a paperclip or, better yet, get a longish (3 inches or more) sewing needle. Very carefully insert the paperclip or needle from the battery side and slowly work it through the central tube until you can see it come out through the central tube on the drip-tip side. Slowly and carefully rotate it a couple of turns, then slowly withdraw it.
This trick amounts to Major Surgery on a carto, so you need to check the resistance when you're done, or you could kill a battery if you've shorted out the carto. If the resistance is roughly 2.0-3.5 ohms (depending on the initial resistance of the carto), then you're good. If it's infinite or zero, that carto is dead. I find I kill about one in ten cartos. But the other nine, after cleaning, then function well enough to reuse. They're not like brand-new, but they're still serviceable.
As always, YMMV.