Mr. Kato, I had similar experience in my 190E, 2.6L, 1988.
The fuel door actuator could be the culprit. It cost $25 at: FINISH LINE , MIAMI.
The driver door lock in my car is failing like yours. I need to reemplace the lock only, but the MB dealer ask me the car's original property documents for salling the lock. It cost $88.
May be you don't need to change the electronic cilinder key. It cost $300, only can be sold by MB dealer.
Please first at all, check for any vaccum leak.
Take care with the vaccum pump it cost $300.