I think the bi metallic evap was used throughout the series, but I'm not sure. Although they are bad about going out, it does not mean that it is totally inevitable. My '88, knock on wood, still has the original evaporator and is still tight.

Components often get such reputations when a high failure rate is experienced, but a high failure rate can be 15%. It does not mean that such a component is destined to fail.

The worst thing you could do would be to run and replace the evaporator the first time the refrigerant is low because you ASSUMED that it had failed. A few months ago, my system was empty after the winter and I was getting pretty close to changing it. After looking the system over more closely, it became apparent that the expansion valve was leaking. I pulled it out and then I could see that had been leaking PROFUSELY. I replaced the expansion valve and the system is VERY tight.

The more expensive and difficult to replace, requires even more thorough diagnosis although you should always thoroughly diagnose before replacing any component, even if it's a fifteen cent component that you can replace in 30 seconds. Just throwing parts at a problem without thorough diagnosis is a very bad and expensive habit to develop.

Good luck,