Also dealer item. $2 or so.
Fastlane has it too.

And.... they do need to be vacuum tight.

I actually made my own.

Model car tire and a dime as a cap, then some black RTV.

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80 300D 340K Owned 30 yrs
83 300SD 440K Owned 9 yrs - Daily Driver 150mi/day
02 Z71 Suburban 117,000
15 Toyota Prius 2600 miles
00 Harley Sportster 24k
09 Yamaha R6
03 Ninja 250