Its No 3 that I was querying, since I couldnt see where or how it was connected, and what looked strange to me.
As an aside - No 4 the lantern - is it a PIR device? These are very well known to cause problems with adsl.
Also - is it possible for you to remove the filter, undo the 2 screws and take a photo showing the internal wiring of that socket, just so we can have a look and check how its all connected up.
I like to see where inside the box, and also how the extensions are wired up to the reverse of the LJU2 - kinda like
this but showing the wiring.
As regards to an NTE-5.. thats what I was saying you needed the bt engineer to do last time he was out at your house. Otherwise I believe the charge for "normalisation" of you master socket to an NTE5 is £25.
The other option is the DIY version which roseway pointed out at the bottom of
this page.
As dave said, you cant actually to a straight swap for an NTE5 unless its done by a BT engineer, they will know if youve done that... because only a BT fitted NTE5 has the official Openreach logo.
However, you can "piggy back" to a new NTE5 located right next to the old LJU2 - see the pic on the above page on how to wire it.