I've heard of several folks having that issue and experienced it myself on that yellow foam deteriorating. Fortunately the one I had do it, I had a thin sheet o plastic film between the foam and loco so no harm came to the engine. I've not seen that happen with the foam that is like what M/T is using so I agree with Joe that is shouldn't be an issue.
AHM HO Scale locomotives were often packaged in the yellow foam mentioned-- which is nothing like the black foam that MTL is using. A number of my late father's locomotives are caked with this foam and are likely total losses. Dispositioning them is a project for the medium to distant future.
