Send it out,
I wouldn't dare work on the internals of the USP. I have asked local smiths and all have said they cant do anything for it, so take it to someone that know what their doing.
Bruce Gray of Grayguns, or Bill Springfield of Trigger works, those are the only two I know of that work on USPs and are reliable, Grayguns is somewhat of an expert and Triggerworks will do work fast and cheap, search him to see the latest opinions on his work.
Jake