It seems that the older models had a problem that was fixed. So, the tip needs to be tweakws a bit.
If you have an older model, store the pieces separately in order to prevent the rubber from being under constant compression. If you have a newer model, push the piston all the way in until the end of the piston pops out the other end. Oh, and that is only possible if the cap isn’t screwed on. That piece needs to be stored separately anyway.