There must be something going on about the properties of radiator fluid that you're not getting.

Every website that deals with radiator fluid says that it becomes corrosive when old.

If you do a google on coolant, you'll get a ton of hits that says that it is corrosive.

Here's one:

http://www.canadiandriver.com/articles/jk/at_001212.htm

__________________
Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".