Wrong coolant causes problems?

A frustrated friend of mine just asked me for advice about his car... a '95 Lumina. The car is in the shop for a coolant leak near the front of the engine (bad enough that he cannot drive it). The mechanic is saying that he used the wrong anti-freeze/coolant and this caused his leak. He said he should have used "Gold Seal" coolant instead of the regular "green" stuff ... the mechanic wants $500 to fix his car. I may be wrong, but this just doesnt sound right to me. Anyone ever heard of this?

Yes in fact using the wrong coolant can cause problems major problems due to the mixing of different coolants and different chemical makeups in coolants $500.00 sounds outrageous for an external coolant leak. The car will need a coolant flush Id reccomend letting the mechanic do this seeing as two different coolants were mixed. But the price should be no where near $500.00 for the repair and flush look for mid 3 hundreds on the most expensive end. Take your car else where!!! Alot of mechanics dislike the Lumina therefore will bid high on jobs!!!!!!

We didn't know what to put in my cutlass, so we went with what the dealer recommended (which was dex-cool). Ruined my radiator and required a major $1200 fix.

Bottom line, don't mix coolants :P