Last August, I had my local Mercedes dealer replace all the tyres on my Wife’s W169 (A-Class). She typically drives less than 5K miles per year. All was fine until last December, when the front near side front tyre deflated by exactly 7 lbs, causing the car’s deflation alarm to trigger. I had Mercedes check the tyre. No obvious problem was evident. Fast forward to Easter 2018. The same issue arises on the same tyre: deflation by exactly 7lbs. Again, no problem reported by Mercedes on inspection. I had them replace the tyre valve, just to be sure. Yesterday, the same issue manifests itself again. The tyre deflation alarm triggers while driving. The same problematic tyre shows deflation by exactly 7 lbs. Weird, right? Why just by 7 lbs in each and every occurance? In talking to Mercedes, my options are - replace what looks to be a ‘problem free’ tyre (since none of their usual tests reveals any problems). Then, if the same issue subsequently arises, I will need to replace the alloy wheel. Given the car’s low mileage, and the relative newness of the tyre, I’ve also asked Mercedes to submit the present offending tyre to Continental for testing. IF they discover a problem, they are likely to proportionately refund the cost of the tyre.