[Arran]

I think that you can actually service those copper oxide rectifiers, they are a series of washers held together with a bolt, so you could try tightening the bolt to see if that helps, I'm sure there is better info on them then I have. Selenium is different, they degrade with age, they are also for high voltage low current applications whereas copper oxide is the opposite, low(ish) voltage and high current applications. The original surround, or hinge, was probably made out of a leather or chamois material which has dried up and fallen apart, you can buy a chamois for cleaning cars and cut it up for a replacement. The cone looks fairly simple to replicate, but I wonder if the cone speaker specialist has any replacements, Mr Chidester I think is his name.
Regards
Arran