Coolant Changeover (Green Stuff to Zerex) Question

[shertex]

So, I'm due for a coolant flush. My car currently has the "green stuff" in it (from a radiator replacement two years ago). But, having read all the posts on coolant, it seemed to make sense to go with MB Coolant or Zerex G-05.

Was no small feat finding the Zerex, which I eventually did at a local Napa. But as I'm walking out of the store, the guy behind the counter made the comment that it is not advisable to switch from the green stuff to the Zerex (or similar) products because of chemical reactions/corrosion that will result. His contention was that, even if you flush the system, the metal parts have already reacted to the green stuff in such a way that, when replaced with Zerex, accelerated corrosion will result.

Granted, it's just some guy behind the counter. But it did unnerve me a little bit, so I thought I'd ask you guys.

Thanks.