Thank you very much for these insights.
So there is a wax box built around the bobbin case? Is the screw on top the filler cap?
I am actually on my way to stripping all the paint from the major parts as there seemed to be some paint spillage or similar all over the machine, and the original paint is chipping too.
I will wire wheel all the major parts to bare metal and repaint them.
Luckily the insides are in good condition. I will not disassemble the main mechanism, but I will clean it up good with solvents and regrease and oil where needed.
I will most likely be using pre-waxed threads, so I will disconnect all the heater wires.
I will also be converting this machine to a modern servo motor, so there are a lot of parts I can leave out from the reassembly, like the power switch, heater switches, motor mount, power transfer wheel, etc.