Please help I'm in Radiator hell

[denali]

Hi, I live in seoul, Korea one of a few 318ti ownwer here
I purchased a 1995 318ti (48900mile-but i can't believe) last week by dealer. It has a good looking both exterior.

but the radiator leakage (I guess) makes me crazy now.
I found some leakage a few days ago. first I added WAKOS radiator stop leak
oil but It' won't stop (little bit better)
I examined radiator and found the problem is not radiator coil, but some
linking point (it looks like plastic part, plase see attatched pic)
and yesterday I operate some epoxy clay(miraclefix) on that but still leaks at the same point(seems coolant go through the epoxy)

I found the part that is supposed to be the 'problem point' at realoem.com
but there's no exact name of it (maybe 13,14,9 please see pics)
where can I buy this part or have any solution? in Korea bmw offical service
costs to high(even windows wiper exeeds 100$)

Is there anybody who suffered the same problem with me?
Pleas help me. I wonder If I buy a new radiator and replace it or just
replace coolant expansion tank, or just thighten some bolts.