Paul gets it correct.
If you had checked on WNXX it has the Class 06 disposal locations and 06005 and 06006 were cut in in Dundee in July 83. - gave enough clues to work it out.
I presume it's somewhere on the riverside. Probably under the Tesco car park now?
Open floor as I have nothing to contribute unfortunately.
Tilbury?
Seaforth
Sunderland Docks