I had given up on my GH with it's spotty performance and difficulty getting it to stay blue for long enough. It's almost 4 years old, no RMA either.
I spent a few days working on the back end and cleaning the threads but what works best is just twisting the back end until it works. Mine does not feel as smooth as it was when new but it is working again and pumping out vapor!
Lots of twisting, pushing and pulling and banging the clicker on my leg seems to have done wonders!
Also have a new back end on order.