Internal workings of a NAVTEX mushroom H antenna?

[Franziska]

Hi,

we have a fully functional Furuno Nx-300 NAVTEX unit.

Self tests are ok and it has occasionally received something when we where close to Lisbon, but not nearly as much as before.
All stations and message types are on.
We are in the Mediterranean.
We can hear the receive notivy sound and it sounds correct as when an RTTY/NAVTEX message comes in.
We did not add other electronic or electric devices since it has been receiving good.

It looks like the NX-3H antenna seems faulty.
Probably a chafed cable inside or a bad connector.
Cable leading to the housing looks ok though.

First step will be to cut 2cm off the connector end and resolder the coaxial connector.
Does anybody here happened to know how to open up the antenna body and what to expect inside?
Apart from a chafed cable, what could make such an antenna faulty?

A new antenna or sending it to a repair is not an option.
Both is extremely expensive, the latter is likely to result in a buy a new one answer despite the cost.
As we have time we are willing to try to fix it ourselves. Still someone might be able to give us a heads up as to how to open the housing and what to expect inside.