AM returns to the Prius radio

More than three years ago, the AM reception on the Prius's (2005) radio failed, no stations could be found; all I got was static. As an avid listener to the BBC World Service (648kHz in Holland), this was annoying, but after the local garage had told me the costs of discovering the problem (and more than likely having to replace the radio) I came to 'kind of' accept it.
I write 'kind of' because I searched the internet and quite a few posts mentioned that it was nothing other than an aerial or coaxial cable (between radio and aerial) problem. Unfortunately accessing the rear of the radio means taking the dashboard apart.
Well, a couple of weekends ago, I was sat in the car, waiting for Sophy's swimming lesson to end. With a small hour to spare and nothing to read (I'd forgotten my book) I gingerly started taking the dashboard apart.
My initial discovery was that with a bit of force, you soon discover which sections have to come out first and which of the three fastening methods are employed: screw, plug or bolt (only for the radio and monitor). So when Sophy returned from the swimming, a bit of the dashboard was lying on the back seat (to Sophy's surprise).
The day after (Sunday), I decided to continue (otherwise nothing would have been gained). The result:

Note that my excuse to the family ("oh no, Dada's taking something apart, again") was Christina's discovery that the CD player had stopped working as Sebastian (at a younger age) had inserted coins in the CD slot. So after taking the radio module out I managed to get the coins out (not through the slot but the bottom of the unit):

(I'm rich !!!). Unfortunately this didn't solve the AM reception problem. Bearing my maxim in mind that most electrical failures are caused by mechanical failure I tried the obvious; the connection of the coaxial (antenna) cable to the unit .. unfortunately powering the radio up didn't make any difference. (Here's the rear of the module, note that not all of the connectors are used (unfortunately I didn't make a note which one wasn't used (presumably for a telephone)):)

Anyhoo .. I traced the coaxial cable (which head's out to the passenger side and up the A pillar (behind the airbag) under the roof to the aerial. It's there that I noticed the bolt which holds the aerial in place and which also (presumably) earths the aerial (sharp teeth on a ring under the bolt) to the roof and thus the car (view is looking forward from the boot, under the roof lining (which is held in place with three plugs)):

Tightening this bolt made a big difference !! (Note that the reception still isn't as good as it was originally, I have to crank the volume up, but I can once again listen to the World Service).
While I was at it, I also took the aerial apart (see if this was all wired up OK) and was surprised by the electronics there (see where the white core of the coaxial cable comes up and the copper wire is connected to the body of the aerial):

Note that after putting everything back together caused a slight panic as the (auxiliary) battery seemed to have drained (I'd had the radio on (loud) for quite a time ??) and after recharging the monitor displayed a warning 'Problem' with no further context. (The car could still be driven, but it left me worried). After dinner though, I went for a test drive and the problem / warning had disappeared .. phew. (I can only think that the charger I use for the auxiliary battery is too powerful .. possibly overcharging the battery ??).
Anyhoo .. said the preacher: don't be afraid, a lot can be achieved and learned by taking things apart.