Most likely, the thin plastic diaphram on the back of the bubble needs to be repaired or replaced. I just put a layer of silicone sealant all over the back of mine, but other people have come up with other solutions (such as cutting out a new thin plastic diaphram from household stuff).

For slow responsiveness: fill with glycerin
For quick responsiveness: fill with mineral oil

A caution on the glycerin substitution: That's what I used when I redid mine over the winter and I think it's starting to make the paint on the indicator dial bubble up. If I had to do it again, I'd go with mineral oil.

I'm surprised a search turned up nothing. Must be the new system. This is a regularly posted topic.