Dexcool in '93 Roadmaster Wagon

To make a long story short - if I can! I had my waterpump on my '93 Estate Wagon replaced at the local Buick Dealer this week and since it was almost time for it, I had them replace the engine coolant at the same time. Turns out they put in Dexcool (instead of the green coolant which had been the fluid I've used since the beginning of time.) They said the Dexcool was what they used exclusively now and it wouldn't harm my Roadmaster. (120,000 miles on the clicker) I've since done some research and found that the Dexcool might not be so cool for my engine. The dealership offered to flush the system and replace the coolant with new green coolant at no charge if it'll "make me feel better." What would you folks recommend I do? Is the system going to be contaminated now nomatter which color of fluid I use?