Okay - thanks. That confirms then that its probably not a fault, but inherited in the car design.
So an inline booster will be the solution. Looking on eBay there are basically three types - the inline requiring the antenna cable to be cut and DIN plugs soldered in back close to the antenna, or the sharks fin with inbuilt booster, or there's a long antenna rod similar to the OEM antenna with inbuilt amp in the base.
Has anyone had experience with the the shark fin style or OEM style replacement?