How worn is the screw? The barrel?
How about the bar slides?
Who was their repair man or shop for parts? Are parts still available without having to hunt to the ends of the earth for them. 70's electronic parts are not the easiest to come by. Does it have manuals and schematics (KEY here)? Without schematics you will not be able to figure a whole lot out if you have problems.
Are the tips replaceable? If so when was the last one replaced? What thread style?
Just because a company is in business do not assume they still sell parts for them. Do not go for the 'the company is still in business' and be satisfied. You need to go forth with the effort to check this stuff for yourself and see how much rates are if repairs are needed. They may remanufacture parts for you, but at a premium.
Do YOUR homework on the machine! If you can physically look at it do so.