Not the tiles, it is the tin flashing's fault.

It seems the joinery section of my roof's flashing is made out thin TIN and it is rusting as we speak. To me I knew something was up but I could never put a finger on it, as I am not a professional in roof repairs and no I did not learn about it in High School. In July I have called up a few roof tilers and got their opinions. The second one made the most sense and gave a decent recommendation to have a plumber to replace the whole flashing during summer-autumn time. Indeed I will. For now more silicon glue was inserted to the leakying spot. Well, that is what you get for living in an old house is 20 yo.

Extra Info:

http://www.askthebuilder.com/

http://www.ehow.com/video_4419521_check-reseal-roof-flashing.html

What does a flashing look like?

A roof with weak or bad flashing.