http://www.nyelubricants.com/lubenot...edBearings.pdf

Ester-based oils may adversely affect some plastics, such as ABS, polycarbonates, and polyphenylene oxides. If compatibility questions arise, contact Nye Lubricants prior to lubricant selection.
In hind sight, perhaps a different word would have been more fitting.

SAE 50W is much more viscous than 10W and is understandable considering they are built to different tolerances.

Note GM doesn't recommend changing the S/C fluid.

That is because this ester based fluid is designed as a lube for life solution.

If someone wishes to switch to a non lube for life system in aims of improving performance, that is their prerogative.

A similar issue arises with spark plugs.

Iridium is the factory solution. A long life product.

Copper is the modder's solution. A short life, higher performance product.