VW Bora Coolant Issue
 

Hi guys i have a 1.9 TDi VW Bora Sports and a month ago i had a coolant warning light come on,i topped up the header tank but the level would drop every week or so.I had it pressure tested and was told to change the header tank which i did.It has recently done it again so i put some bar seals in,lo and behold it is still happening!!.The car is 10 years old has 116000 miles on the clock but still drives superbly,the temp stays normal too.Any ideas on what could be wrong? it would be most appreciated...Kev.