88, you do realize that Dell uses local contractors for their warranty repairs, right?
This means the guy gets paid when he fixes your unit and you sign off as satisfied.
Call Dell, rather than use chat. Describe symptoms that reflect a failing screen. If you're still in warranty, they'll dispatch a repair.
The contractor that responds has no incentive to balk when he gets there with the new screen and sees yours is cracked. He has every incentive to just replace it, scrap the old part, and collect his fee.
I realize this isn't a model for honest behavior, but I wouldn't suggest it if it didn't sound as if you deserve the repair and the reps you've approached aren't doing what's right.
culero (administrated a lot of warranty in his day, its all about how you write it up)