MGTF “Duo” or Fiat rear lights

We particularly like these rear lights on our TF but now realise that they are now a liability. If you look at the photos you can see that they are gradually “unbonding from the body shell. This has all happened in the last six months, it has gone from a tiny rust spot to what looks like continuous rust under the fibre glass and filler. Does anyone have any knowledge of how these were fitted? Or who supplied them so that I can get more information as to how they were fitted?
It appears that there is a fibre glass moulding that is bonded to the body shell and made good with bodyfiller. The lights themselves are just held in situ with silicone mastic. My option seems to be to remove the light and then try to pull the fibreglass moulding off. I could leave it for another six months to see if it continues to become detached but at the same time want to stop the rust that is obviously underneath. All suggestions gratefully appreciated. 

The only way to deal with that rust is to completely remove the lights, the cover and all the silicone shit to get back to the bare metal. The rust then needs to be dealt with.

If the removal is done with care the tail light conversion might be able to be saved. But that's a very big MAYBE!
I suspect that it wasn't done properly in the first place, with shitty workmanship, they probably sealed rust in under filler.
Another possibility is that the filler used is too rigid to deal with the body flex causing it to crack and let water in which in turn causing rust, a more flexible filler would be required or sufficient reinforcement applied to the area to prevent the flexing, the problem with that is that you might just transfer the problem to the next weakest point.
Probably easier to go back to using standard lights.

Yes that is the whole intention, although the Duo lights look really good I know that there is no way of saving them. Its just finding a way to remove what it there with the least damage, I am suspecting that they are fitted with an expanding polyurethane adhesive rather than just a resin bond. I will probably take the plunge after I am given the okay to return to "work"

Why not buy a couple of crap standard lamp units & fit the Fiat lamp units into them. A hole saw of the correct size to cut your holes , then polypropylene plant pots to create a inner surround & a base fixing if judiciously executed.
Twenty five quid a pair on eBay, if you were to pick them up from Southend; more to your door.
Just a thought.
M

You can see here the normal quad rear light setup. i.e. Not bonded in!

Thank you David, the ones fitted to our car have no fixing bolts or screws. There is black mastic around the original holes in the steel panel which I pulled off and dismay found that it was sealing water into the area. I will get a pair of used ones and take the plunge in a few weeks time.