Thanks for the tip on the wheel. We did check the spare, which was MB. The trunk looks like it was never used, actually - the original owner was an older woman who apparently didn't drive outside of a small geographical area.

BTW, is the spare just near-full sized or is it actually full-sized? It's definitely bigger than the "minis" I'm used to on cars. The owner's manual suggests mounting it on the rear axle if possible, which leads me to believe it is somehow different than normal tires, but it also doesn't say you need to go out and buy a new one to replace it ASAP as my old Taurus, with a minitire, did.

You'll have to forgive my ignorance here, as my experience is mostly with a bit newer American-made cars.