Ira,
I don't know if (and if so, where) it is in a book.
That is: it probably is - almost everything you can imagine can be found in a book somewhere - but i don't know if it is in one of the well known books on Hasselblad.
Dust and dirt is not a problem.
If you store the back on camera, the camera will protect against dust as well as the slide.
If not on camera, the magazine will of course be empty. Pop the insert out large brush, a quick blow, and it's clean. Very easy, and quick.
I do not know the details of how all other cameras seal their dark slide slots and backs (and mirror boxes and ...). But this thing about foam is, of course, true for all things that use (similar) foam.