Gen5aerial
Common failure is the electric aerial, and I got fed up with mine, so time to roll my sleeves up.
Basically it is quite simple. For £19.82 + VAT you can get a replacement aerial rod from Mr T (part #86337-32200).
Fitting is simple.
Method 1)
Unscrew the large chrome screw/top from the aerial with it down. Then turn on the ignition, let the aerial go up and you can pull it out. You might need to give it some extra help. Simply put the new aerial rod in, teeth will face to the rear, and feed it down, turn off the radio so that the motor retracts the aerial. You may need to turn it on/off a few times for the position to get right.
Method 2)
More reliable but more work
Unscrew the chrome top, and take the whole aerial and motor unit out from below. First unscrew the chrome "cap" as above, then move the boot interior trim - it's the nearside trim that needs to be out of the way, freed up by removing the two nearest screws/poppers on the rear trim (top and bottom) and perhaps a couple of poppers along the top edge. Once free, there's no need to remove the whole trim piece - just get a screwdriver or length of wood and insert it between trim and car body to hold it out of the way.
The motor is held on by a single 10mm nut. Undo this, then detach the electrics and the drain hose from the bottom of the unit. It should easily pull down and out through the access hole.
Also, if leaving the motor in place to change the mast, it's handy to have another set of hands to switch the radio on and off - this saves you running round the car like a nutter to get to the aerial every time. Often, what has happened is the end of the plastic grooved feed has broken off and is stuck inside the motor winder. Thus Method 1 won't work well if this is the case.
You can connect up the aerial motor directly to the battery to make it extend and retract... (simply swap +ve and -ve). Once you have ejected the rod, you can undo the cover where the mechanics happen. Opening this up I saw the broken piece of plastic, removed it, cleaned up the insides, regreased them and back on with the cover.
Put the new rod into the slot, and connect once again to the battery to retract it again into the housing. Fitting is the reverse of removal.
No more than an hour using method 2.