I always throw away the oil cap: A colleague explained to me what it is actually for

This cap always made me angry, because sometimes it has to be pulled out with force and quite roughly, which leads to oil leakage. And sometimes the ring breaks and it is very difficult to open the oil. But not so long ago I found out why it was really necessary.
Now I will tell you everything in detail. The fact is that the plug needs to be returned to its place, but before that you need to return it.

Then press the cork into the bottle so that it is fixed between the slots.

Since the plug is asymmetrical, there is always a small gap.