Long post ahead.
Heres the full story of what i done, though im sure there is a quiker way to do it.
First I removed the plastic stuff from under the wheel arch. To do this you will need to straighten some little metal bits, which are folded over to keep the plastic in place. I just used a pair of plyers to do it.
You will then be able to see the electric motor for the antenna. There is 2(i think) srews that need to be taken out.
You can then undo the wires(which supply the power) conected to the motor, not a must but allows better movement of motor. I DIDNT take the wire which sends the signal to the radio, as it looks like a bitch of a thing to do.
Then look at where the antenna mast protrudes from the top of the panel(into the air), remove the black rubber stopper.
Under the stopper there is a bolt type thing around the mast whish need to be undone from under the wheel arch.
You can now esasily move the motor around, & take it out from under the wheel arch.
You then pull out the old antenna mast, this can be stuck quite strongley. I dont think you have to undo/loosen anything to do this.
Take note which way the thread on the white "chain" in the middle of the mast faces, with repect to the motor.
If you think that all the white 'chain' stuff has been removed, and it is not likely there is any inside the motor, you can slide the new mast and 'chain' in to the motor.
BUT there is usually some of the chain inside the motor. So you will have to undo trhe retaining screws around the motor, and open it up.
Make sure u take note of where everything comes from(unlike me)
Inside the motor will be a series of cogs, and some other little bits. Romove the big cog, and what ever else is nesecary to do so. Under that will be the 'chain' which had broken off. Remove that, and put the motor back together.
Conect the power chords back to the electric motor, turn the ingnition far ebnough so the motor activates.
Push the button, which varies the antenna hight, to the 'high' setting.
Then thread the new 'chain' into the motor. Turn ignition off, or change the antenna hight switch to the low setting.
Hopefully the chain will grap the thread. If not keep trying till it does.
Once the chain has been grabed buy the cogs in the motor, you can force the rest in. Then place the mast into the top of the motor.
Turn ignition on and off a few time to make sure it works.
If it works replace all the bolts and screws. Put thre plastic back under the wheel arch, etc.
You can remove the front left wheel if you want, as it will give better acess.
There is a alternate way to installing the new mast, which involves threading the chain into the motor whoile it(the electric motor) is pulled apart. This can be very fustrating as the new 'chain' isnt bent into the right shape.
Hope thats right, im working from memory.
1st car EA Fairmont Ghia, extractors, exhaust
2nd EF GLi, 'custom' interior, extractors, exhuast
3rd EA Fairmont 5spd, low'd, extractors, exhuast, head
work, 3.45LSD, EL dash, interior+ El ECU
4th EB2 Fairmont, EL dash and interior, BBM, LSD etc etc
5th EB Fairmont Ghia 5L. All leather, lowered, exhaust etc