wez wrx

why are some gear box additives not suitable for lsd? Ive got crap oil in my box (comma full syn) its like water tho its only been in a few months! when the cars cold its fine, but as soon as it gets to temp the box becomes noisey! ive bought a tube of moly slip gearbox protection to try and quetin things down, but on the the tube it states not for slip diff axles? does anyone know why??