Merc Grand M Won't Start

My 2007 GR Marquis has a starting problem. It has 35,000m. A month ago (32,000m), I stopped for coffee and the car would not start. It turned over but no ignition. I had it towed to the dealer. They looked at it the next morning and it started right away. No problem found. Same thing two days later. They checked it right away, saw the problem and changed the crank sensor.

Yesterday it wouldn’t start at all. I had it towed, it started with no problem at the dealers. Today same problem. I am going to have them change the crank sensor again. Anyone have an idea what else maybe going on? These last two days the temperature was around 30 deg.

This is still covered on the factory warranty isn’t it? Don’t they have to give you a loaner until it is right?