if trans lock was securely engaged at the time, it's a no brainer. this is a dealer/warranty/liability issue. just think if someone were standing around & got hurt...don't let any guilt trips they try to impose on you set in. insurance companies have the same mentality as your dealer on incidents like this that makes them look bad.... you're in the right & potentially have lawyers to prove it. best of luck on repair. i've had several QC issues on new machines . fortunately, my dealership was glad to follow through. one would think all dealerships would have the brains to at least check safety issues before they release a new (or used!) machine..... keep yer head level and pursue what is rightfully yours...
also...if this really looks like a problem w/your dealership, you might consider an independent source to look at the cable adj. and verify/document before turning it over to them. from this point, i'd document everything incl pics... sorry to seem so skeptical of dealerships, but who's to say they would fix the trans lock, deny any problem, then let you pick up the 20K repair. stranger things have happened.