Tire losing air, don’t know why.
Wife picked up a 2014 E350 4Matic a few months ago. I noticed the front passenger tire was slowly losing air every three or four days. Only about 3 to 4 psi. Brought it to my local Euro shop and they found a nail in the tire and put in a plug. I also had them set all the tires to 40 psi. So the very next time she drove the car after the plug the light came on and the tire had lost 10 psi. I thought thats weird so I pumped it back up to 40 psi and the next morning the tire was again at 30 psi. So I brought it back to the local euro shop and had them reinspect the tire. They said they cannot find a leak. The plug is good. They even took the tire off and put it in some bath to see a leak and nothing. They just threw their hands up in the air and said who knows. I didn’t have time to leave the car with them to search further. What’s going on? When the tire is off the car the leak goes away? And the strange part is it seems to stop leaking at 10psi loss. I’ve been driving the car for a few days after getting it rechecked and the tire is holding steady at 30 psi while all the other tires are at 40 psi. Is it a rim problem? Tire is messed up after they did the plug? The bead on the tire bad? I’m stumped.