08 MB ML 320 CDI central locking /tailgate lock challenges

I’ve got a problem related to malfunctioning tailgate lock on my car. Since my dog is always with me when I go for a drive I need to have an opening possibility that I can trust.

1 none of the two car-keys were opening the doors/tailgate

2 drivers door manually opened and the central locking was operated with the switch inside the door.

3 for a short while when parked the tailgate lock appeared to rapidly be switching on/off and operating the central locking door key didn’t had any impact on this.

4 the tailgate was locked/couldn’t be opened.

5 the red warning “tailgate open” was illuminated when I was driving despite of the fact that the tailgate was closed.

6 I made several attempts to opened the tailgate when I was back home again to get my dog out. Could hear a “sound”, but the tailgate was locked.

7 I waited 15-20minutes and tried again and then everything was operational again

8 visited a MB garage - no error-codes had been registered in the diagnosis system.

Problem now is that the tailgate is fully operational, but I don’t trust it!

All suggestions will be highly appreciated!