Part number for plastic part that connects seal from spoiler to the trunk

[pascalgerber]

As it seems, I am looking for a very hard to find part. The problem is it is difficult to describe what part I mean.
 

I was replacing the third brake light. While disconnecting the cables to remove the spoiler, I apparently broke the plastic part that attaches the seal pipe to the trunk. This seal pipe contains the cable for the 3rd brake light as well as the washer fluid pipe.
 

Now I want to replace this plastic part, but can't find a part number anywhere.
 

The part can be found as follows: if you open the trunk you can see two wiring harnesses at the top. The left one is a bit elongated, the right one is round. And exactly at this right attachment this round plastic part broke.

Does anyone knows how I can find this part. Since english isn't my mother language I cannot figure out how this part is called.

Thanks for any support.

[newdude]

I would call it a grommet or retainer.

 

Having said that, unfortunately you cannot buy that part separately.  It is sold only as a part of the third brake light wiring harness.  Part # 23211598 is the harness.  

[cs15dah]

eBay has two right now. Both are less than $30 with shipping.