Corrosion of Magnesium with Unpassivated SS

There is a good chance that the magnesium will be corroded in contact with unpassivated stainless steel. I suggest to read the former discussions about aluminium.

Magnesium is one of the least noble metals used. You can even burn it. Edwin Muller
KEMA Power Generation & Sustainables
Arnhem, The Netherlands
E-mail e.f.muller@kema.nl
Internet:

It is inadvisable to connect any stainless steel to a magnesium alloy if there is a corrosion source and electrolyte. This galvanic couple will result in rapid corrosion/dissolution of the magnesium.

If you need to have a SS component in contact with a Mg component, you will need to address the galvanic corrosion potential. Coatings can be used to minimize the problem, but a great deal of attention must be paid to details like anode to cathode ratio, coating damage, etc.