Need to replace rear windshield gasket - or how to get a price quote from dealer

[bigmaq]

I have to replace the rear gasket on my rear windshield. It's $150 labor at Safelite + $150 OEM MB gasket. That total is almost as much as it was to install a new front windshield from Safelite (with all parts and labor--been happy with it btw). Since the total was almost as much as new installed, i thought might as well install a new one. So I called Safelite but they don't make a rear windshield for my 300SD and said it was a dealer-only item. I tried to get a quote from the dealer to get new gasket installed, but they're always reluctant to give you a quote because you'll probably drive away as fast as possible to an indie after you hear their price. Dealer wants you to drop it off so they can look at it then give you a price later. They know you're less likely to run away if your car is already there.

So two questions:
1. What's the going rate for a dealer to install new rear windshield gasket? All I could get was about 2 hours labor x whatever their labor charge + parts.
2. Why don't dealers like to give price quotes unless you drop off the car?