How easy it is for MoS2 to become oxidized
It seems that the problem has been examined even 50 years ago, probably in order to determine if/how oxidation would alter the the properties of $\ce{MoS2}$ as a lubricant.

Here is an old NASA document from 1949, and in Surface Oxidation of Molybdenum Disulfide from 1955, the authors state in the abstract, that the oxidation is limited to the outmost surface layer, which then passivates and protects the rest of the batch.