Gear Oil

A few replies have said not to use syn oil. Other than 'opinions', what evidence is there that it causes problems.
My GTO also has a cone type LSD rear axle. It had slight gear whine when coasting. I tried two mineral oils with the correct LSD additive, made no difference to the whine.
I then used Redline 75/140 syn & it almost completely eliminated the noise. Twenty six years later, still using Redline & zero problems.