Sounds to me like the GM dealer is full of crap!! If the car was brought in with the top "stuck" in the trunk they couldn't possibly have diagnosed a hydraulic hose leak...and if it is, in fact, a "hose leak", that's an easy fix.
1) Is there an error displayed on your radio?
2) Enlist a strong friend or two to help you lift the top out of the trunk and put in top up position (doesn't have to be latched closed).
3) Remove the passenger side trunk trim panel in order to get to the hydraulic pump. Unplug the trunk light and convertible top position switch from the trim panel.
4) Check hydraulic pump to make sure hydraulic fluid is at proper level. If not at proper level, you have a leak somewhere.
5) If (4) above indicates a leak, inspect the hydraulic rams and all hydraulic hoses for leaks. The main rams are notorious for seals going bad and leaking.
6) Inspect all convertible top wiring, especially around the hinges, for any split or exposed wires.
I'd start with the above and report back here as I'm sure one of us can assist with further troubleshooting....you won't get much help from any GM dealer.