Pontiac Repair: Coolant, coolant leak, ac delco

Question
Should I replace the coolant that now is Dexcool in my pontiac 2000 sunfire 2.4 with the green or yellow aluminum compatible stuff. I hear that the dexcool is corrosive and if the water pump gets changed I can then replace the coolant as long as all the other is out of the engine. I have a small puddle weepage so more than a few drips under the car in the morning after it sits a few hours. But not if it only stands a couple of hours. I was told by Todd to replace the water pump with a new ac delco with a weepage holder that is supplied with the new pump. And also how ofen are you supposed to change the timing chain. This car I bought used at 159,000 kms. Thanks Warren

Answer
so long as the dex cool has never been cross contaminated i would put new dex cool in, only issues have been with cars or trucks that have a coolant leak that is never repaired then it gets ugly.  as for the timing chaing we do not service them till they break but i would say 100,000 miles would be a good time to replace it