1996 960 wagon

I need to know the name for this part so I can find / replace it. It is leaking...

Left side - top of radiator - looking in from front of vehicle. Little rubber cap that seals what I so far understand is the expansion tank outlet (?) ...It is affixed with a simple hose clamp.

Should be an easy fix, but of course I cannot find a simple name for this part, nor does it appear in any diagram I can find.

tia =)

 

Better post a picture--much better to show what's going on and get help!

 

If I understand correctly, I call it a block off plug. Most part stores have a "HELP" (brand) parts section. I find them there and have been using them for years when restoring old cars.