Oh, looks to be in very nice condition!
I think its an original plinth. If you are in the US, there were a couple of companies which made plinths for Dual turntables, since some of these were shipped without a plinth.
It might be a rare plinth, I will let someone else chim in.
As far as for servicing it, I would strongly suggest doing a full restoration. I did it on mine 1019, and it spins without a problem ever since.
The motor constantly running was an issue I could not figure on mine. It was not dried lube, so I let the technician solve the problem. He was not home when I picked the turntable, so I am still not sure where the problem was.
In regard to service:
The whole mechanism on the bottom can be divided in three sections:
-Idler mechanism and motor. You can disassemble just the idler mechanism on work on it. There is a spring right next to the motor. If detached it will let you work on just that part.
Its not that hard. Disassemble, clean and reassemble. And it might be worth taking some pictures. Careful about those springs. They like to fly off and take the washers with them.
There is a lot written in the forums about which oils to use. For the idler wheel and platter shaft use adhesive oil
, it must be safe on colored metals
. Originally ISO 68 was used (Renotac 342), although you might want to try ISO 100. Always clean all the old oil. Some oils if mixed, will make a chemical reaction after some time. You dont want that. Sintered bearings require some extra patience. Isoprohyl alcohol is a good way to remove the old oil.
You can also sand the outer edge of the idler wheel, that way you remove the hardened part of the rubber .Dont go crazy with the sanding, remove just enough until you can see the dark rubber underneath. The idler wheel needs to be slightly tipped >. Easiest way to achieve that is to fix the idler wheel on a drill and then use some sandpaper glued on a piece of wood. I would recommend the finnest grit you can find. You want the idler to be as smooth as possible.
Next you can move to the cam, tonearm mechanism and finally platter bearing. Leave the motor until last. That motor does not like to be upside down (oil leaking from the bearing making it dry).
There are full service manuals on the dualcan site for the cam and motor: