I feel the need to reply here..... being used to Rovers and water leaks

Ok, rad weld style stuff is ok as a temp fix, but i would never bung that crap in my car tbh.
If your expansion cap does not fit properly then you could well be losing coolant from there, if the cap does not hold pressure then the coolant will boil too early and pressure and steam will escape, although you should see evidence of this around the expansion tank and cap.
Why do you ask about a specific place on the rad (is this common on this car) if your rad is leaking then why trade it in for another car ? just replace the rad lol, cant be more that a ton ...
Hmm i just read the post properly, second hand rad if yours is leaking, rad weld i suppose but thats a fair few months for a temp repair imo