This happened to me. A week ago typre pressure light came on. Checked all tyres. Rear offside was low (27psi instead of 37psi) but not puncture or damage. Reinflated and drove on. A week later, the same warning light came on. Checked the pressures and same tyre had dropped the same amount again. But this time I found a nail in thr rear offside tyre. Just out of range of repair so getting a new set on the rear.