I have several Fbody Lt1 equipped vehicles. I JUST changed my 95 Formulas ORIGINAL opti at 271k. On my 94 Z it went 180k on the original opti, one was a vented style (95) the other was not. The 94 is being built as a street/strip machine and is being changed over to the vented style opti. Time will tell whether or not I will change to anything else. I have personally never had a proble out of a GM unit, only once from one that I bought that was not GM, BUT ADVERTISED AS SO.........