Puma have you tried disassembling it? It's fairly easy to do. Once you do, try some plastic part friendly grease on the ball and spring and some of the other lower internal moving plastic parts. That fixed the same problem up for me with mine. That said, getting a replacement ring/washer may be required, I've read guys who have posted that within less than 100 hours of use it's worn to the point that it's causing huge problems.
I bought a replacement ring from a dude on Warthog World who charged me 8$ for a PTFE teflon tough bellybutton ring accurately cut with a C02 laser system he has access to. That included shipping. It's usually a part, that oring from TM, that gives a lot of headaches and causes most internal problems IMO. That couple with good grease, and I've never had an issue since.