Has anyone used Amsoil synthetic Transmission lube 75W-90 GL-4 in their 1969 4 speed?

I have used AMSOIL and will never use it again because this produce took out my trans and the AMSOIL company would not stand behind their product. They spend more money testing and retesting their oil sample that was drained from my 4-speed with less then 500 miles on the rebuild that they could have rebuilt it the trans two times. They also conveniently lose the particles and filter that I shipped to them and then said they could not find any trace of metals in the oil sample that was shipped in the same box as the particles and filter. Companies like this should be put out of business.