Major Hochstetter's car has a different license plate on front & back. The car is filmed several times in this episode. The front plate is WH 38495 & the rear plate is WH 54693. There are either two different plates or they were using two different cars.
Maj. Wolfgang Hochstetter:
Until we catch those traitors, Stalag 13 will be under Gestapo control. No one in or out without my permission.
Col. Wilhelm Klink: Uh, what about me?
Maj. Wolfgang Hochstetter: You may come and go as you please, Kommandant. Hopefully, you will go.
In order to set up the second scientist's escape, the prisoners cause a coolant leak in Hochstetter's car. In order to fix the leak, Newkirk asks for a hammer, which can be found in the trunk of the car. The scientist goes to get it, but, instead, crawls into the trunk. After the car is repaired, Schultz demands to know where the prisoner sent to get the hammer is. LeBeau turns up with it and gives the hammer to Schultz. The problem is that, since Schultz overheard the request for the hammer (as he was supposed to), he would also have overheard that the hammer was in the trunk. Therefore, the obvious next move for Schultz would be to put the hammer back in the trunk of the car - thus revealing the scientist hidden in the trunk.