A few things to check:
Make sure there's plent of lube (Dow) on the o-rings in the bolt chamber, and on the bolt itself but not in any of the holes. Is the gun still firing, or is the leak causing the bolt to stick?
Solenoid gasket. I had my '03 with Phil down at SP for over 4 hours before he found that this was the culprit. Be careful as you unscrew all the tiny bits of the solenoid, as they're so small you can lose them by sneezing.
The o-rings down the RIGHT side chamber (as you look from behind the gun). The one furthest forward can dry up or worse still, split. They're tiny, so be careful as you take the long pin out. Lube 'em up good when u put them back in.
If you've had the input pressure too high, then it's possible that you've blown the solenoid. Since you say you've been using it fine all day, then I'll assume you haven't changed the input, so it'll be something simple like one of the orings or the gasket.
Skeet: the '03 doesn't have a valve as such... the valve is built into the bolt and can be recognised as just.... holes...