Is there anyway I can fix a leaking bleeder or to replace that single part without purchasing a new complete radiator ?

Do you mean the drain tap?

 

If so, yes, you can buy it separately, 6Q0122291F I think. Even better, there's an o-ring inside it that does the sealing of the tap, which is easy to replace.  Somewhere, recently, I wrote down the size of it. I'll just have to remember where. At worst, I have a spare 6Q0122291F at home and I can pull out the drain tap and measure the o-ring again.

I'm sorry for my writing, I'm not a native english speaker. Yes, I'm talking about that draining tap. It's leaking about 300ml of cooling liquid per day.

Here you go. The o-ring dimensions are given as internal diameter and thickness.  The tap just pulls straight out from the fully open position.

 

 

Removing the tap and replacing the o-ring should be a lot easier than trying to replace the whole fitting.

Thanks a lot !

You're welcome.