My spare was flat and unretrievable w/o a big hammer, probably for years. Might be a good idea to actually remove your spare, check it for proper inflation, and service and grease the rack system.
My ML has a thin space saver spare, 155/90R18, on a sliding rack accessible from under the rear bumper. The rack was all rusted up, the tire stem had rotted, letting the tire go flat, and the sidewalls had pulled way from the rims, screwing up the tire bead surfaces.
The tire would have been OK if I would have crawled under there over the years and maintained the pressure.
The rack pivots in plasrtc hinges inserted in two big holes in frame members. Pull the cotter pin, slide it over and free and lubricate it, if you can. Mine was seized up and wouldn't slide.
I heated up the starboard hinge pin with a propane torch to increase the clearance and now the rack pivots. Verify that the stem is fully astern when you replace the tire so the stem is accessible for pressure checks.
Tire guy has fixed the bead twice but I will need to get a new tire if it still doesn't hold air. Motorcycle tube won't fit as those stems are centered.
They don't use salt on our roads either.