I just recently found out that the power antenna in my 78 Eldorado is not the factory correct one anymore.
My Eldo comes with a radio with the CB option, so it should have the according tri-band antenna for the 78 Eldorado.
One of the previous owners had replaced the original antenna with a replacement antenna, which worked, but it had very poor CB reception and of course it does not look correctly.

What I have found out is that #22010515 was the original part number for the antenna.
This antenna was also used in the 1977 to 1982 Corvette and is extremely rare...
Replacement antennas had the part number #22010661 on the sticker with a date code below.
When these replacement antennas were no longer available, it seems they switched to a different antenna design as a replacement #12355706 (which I had in my car). This last design came with a special antenna splitter. I do not know if this splitter is essential or of it would also work with the original splitter which is still in my car.

It took me quite a while to find the correct antenna for my car as it seems to be made out of "unobtainium". I did search the net for days and somebody sent me an incorrect antenna which was for a Buick… Suddenly during my daily search, a correct, working antenna showed up on ebay, and I immediately hit the "Buy it now" button. It was not exactly cheap, but I was happy to have finally found it. When it arrived I cleaned it up properly.

I then found out that I would also need the correct antenna bezel on the fender. Various sellers sent me incorrect ones which they claimed would be the correct ones, and eventually I found a good used one from the seller of my antenna and a NOS one from a parts vendor (it has not arrived yet as once again USPS sent it to Australia instead of Austria - don't ask what this little bezel has cost… :-( )

I then also had to replace the thinner replacement antenna lead with an original one going from the antenna splitter behind the glove box to the antenna. I got this one from Arizona Vintage Parts.
I can say now that my car is 100% correct again. Unfortunately this project was an extremely expensive project and I will now try to sell all the not needed parts on ebay. They will fit Eldorados with non CB antennas and the other wrong CB antenna I got will be for Buicks, but could also be installed into the 78 Cadillacs, as the mast itself is exactly the same as on the original antenna and from the outside it would look completely stock. But purist as I am, I just needed the 100% correct antenna ;-)

The later style replacement CB antenna which I wanted to replace with an original one.
The later replacement style fender bezel looks completely different from the original one.
On the left you can see the official later style replacement CB antenna which looks very different. It does not have a load coil and no additional stub antenna. This is part #12355706. On the right you can see the original 1978 CB power antenna with the load coil on the mast and two antenna leads and the additional FM stub antenna. This antenna is nearly impossible to find…
Thats the CB - load coil, which can be adjusted. The plastic unfortunately got very brittle over the years on all antennas of this vintage.
This are the instructions which came with the car, if you ordered the very expensive CB option…
The antenna trim bezels for the 1978 Cadillacs. On the left the one for the regular antenna - on the right the one for the CB antenna with a larger diameter in the plastic part. The chrome ring is exactly the same for both. These two are used ones I found.
I cant believe that I was lucky enough to find this super rare antenna bezel as a NOS part - still wrapped in its original plastic bag. Not exactly a bargain, but its 100% perfect.
The new, correct antenna installed into the car.
This is the incorrect CB antenna I got. It could be installed into a 78 Eldorado without any problem and would look 100% correct from the outside. It works perfectly smooth, and the chrome mast is in excellent condition. The load coil and the FM stub antenna are all there. The previous owner of this antenna removed it from a 78 Eldorado, but it would normally be correct for Buicks. If you are not such a purist as I am, you can buy it from me for what I paid for it. ($250 + shipping) It comes with all the necessary hardware to install it.