It just so happens that the TPMS in my Mazda 6 warned me of a loss of pressure in the n/s rear 200 miles into a 300 mile journey today. The culprit was a little bit of metal. I got the car to a motorway service area tyre pump, pulled the spike out with a pair of pliers, then started to follow the instructions for the tyre repair kit supplied with the car. I did everything correctly. Deflated the tyre. Removed the valve core. Squeezed the bottle of latex-like glop into the tyre. Put the core back. Then reflated the tyre, only for the glop to come spitting out of the very small hole in the carcass. So I called the RAC, who plugged the tyre and escorted me to a KwikFit that had the right size (different make) tyre in stock, warning me that the plug probably wasn't safe for the distance I needed to drive. Five hours from the low pressure warning and £254 lighter, I was on my way again. Tyre repair kits are not only even more useless than I thought they were, they are worse than useless, because once they have been used they render the carcass unrepairable. At least a space saver would have got me to a tyre depot with a tyre that could be repaired.