yo dude... I guess I'll reply to your PM here...
Yes SEMI auto problem are related to the cutoff lever not engaging, which could be caused by 2 things (that styrak already mentionned)
1) The cutoff lever is worn out by usage, so it doesnt properly do its work...
2) You're missing the small springs that sit between the selector plate and the cutoff lever on the outside of the gearbox. (see pic... look for the tiny little spring in the middle of the picture, that looks all crammed up)
But for now, just open your gun, and get the mechbox out, and see if it has that small spring....
if it does.... then its a inside-the-mechbox problem, and you'll have to open it up to check inside.... and
if it doesnt, then you'll need to find another small spring to fit in there....
PS: best way to know your gun, is to know exactly how it works...
So, if you want to learn, or already know how to open up your gun, I would suggest you to do it yourself, since the gundock service fees usually start at 20$ per hour... (but you'll be doing it at your own risk, and you could screw your gun....like totally screw it.... so before opening your gun and mechbox, read, watch videos, ask around... (or ask me?))
Hope it helps..
Paul