[Problem with depth drive on hitachi cordless framing nail gun]

UPDATE:

I received my tool back from the Metabo-HPT service center and the nail gun is working properly again, sinking nails perfectly.

Apparently it was a  "X-Ring seal/gasket" repair that fixed the issue.

Also, they did not charge me for shipping or for the repair.

[Problem with depth drive on hitachi cordless framing nail gun]

Same thing is happening to mine. Not sinking nails much more than halfway (using 3'' nails), and a clicking noise which follows. 

Sent in to hitachi for repair, received it back a few weeks later and there was no difference, same problem occurred. 

They claimed that they "recharged air cylinder" and "adjusted nail depth". I believe they did those things, but unfortunately it did not solve my problem. I made the (terrible) judgment call not to get a warranty when I purchased this tool, so I am in a pickle not knowing how to have this tool repaired. At this point I would gladly pay a repair fee if I new the tool could be fixed.