Tire pressure sensors?

To register pressure they must come through a slip ring on each hub, so its how good are the seals and how long will they last. This technology is a by product of motor racing, where the cars are stripped down and rebuilt after every race...........so how long will it last in a car that does not see that treatment. The monthly check is easy and you can then compare figures. Why not let one tyre down and compare the electronic reading to your manual gauge.

Which manufacturers use "slip rings" to convey TPM data? That's the first I've heard of that, as to this point the systems I've read about used on consumer vehicles either use RF with direct TPM sensors on the tire valve stems, or use the same axle rotation sensors used for electronic stability controls and antilock braking controls to indirectly derive inflation status. And those sensors do not utilize "slip rings"...

my Uncles Fordson tractor................

Um, ok. I rather doubt a 40 to 90 year old farm tractor is relevant to the question, but it certainly explains your answer ;-)