Magnesium

Anyone out there know of a clear liquid that could be wiped or rubbed onto magnesium with a rag to keep it from tarnishing /oxidizing ? Not a paint or powder-coat , I get cases bare metal looking really good , but within a few weeks they've turned to a dead dull battleship gray.

I've had the same concern for the polished cases on some of my bikes and through extensive research I've settled on Sharkhide products. Here's the link:

http://sharkhide.com/

The FAQ's have some good info.

Acf50

Vapour blasting magnesium and leaving ir raw lasts quite a while longer

VW on their early Air-cooled magnesium 4 cylinder engines were magnesium and had a Dow 7 treatment which is gold in color https://www.chemical-supermarket.com/Dow-7-Magnesium-Treatment-Compound-p652.html