bazza. Have replaced my aerial with a Mazda unit from a scapper. Dead easy, just remove the trim panel un-plug the old unit remove from vehicle by undoing the 2 nuts on the body work and un-screwing the top of the aerial mast (chrome ring) from the out side body work. You can, just replace the aerial mast though. About £25+ from mazda. You take off the top of the mast from the body work and power the unit up it will push out. You then feed in the new mast as you power doen the unit. Not easy but can be done.
If buying a scrapper unit make sure it's got the same plug as yours as there are a couple of differnt ones about as I found out with mine.
my aerial is busted now... it goes up and down alrite but when it goes all the way down completely it makes a really loud grinding noise which sounds like a chain saw... i mean really loud.