My '05 E320CDI had a flat tire, and out comes the t-spare. Unfortunately the valve stem on the T-Tire split in a few miles and it went flat as well. I will omit the rest of that story.
Problem is: now I cannot find a valve stem for the T-spare anywhere, and of course a new one is hundreds. I can see right now the thing to do is buy a used road wheel and put a tire on it.
Just a warning: because your T-spare has never been used and has plenty of pressure, don't count on it in a pinch.

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1927 Pierce-Arrow Series 80
1931 Pierce-Arrow Series 43
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Is the valve stem hole reduced in diameter? If so, it was also used on the late 00 / early 10 R class inflatable spare. I have a spare that a split the stem just above where it enters the wheel.

I have no idea why a reduced diameter is used. Have a look at valve stems for tubeless motorcycle wheels, I'm pretty sure they are reduced diameter and are usually ( always? ) bolt on.

What size is the temp spare tire? If it was damaged, you could probably find one from another brand that will fit.

If you have space, a standard wheel / tire is the most direct route. Temp spares are only used to save weight.