If you are not experienced, I would consel against buying an old machine, especially from a E auction site, where the chances of being able to examine it are small or non existent.
And as recent Forum posts have shown, there are scammers out there waiting for the unwary.
An old machine will lack the features "normal" to more modern machines, may be worn or damaged, and could have parts missing. Finding replacements can be problematical, even IF a part can be found. It may be even more worn or damaged than the part that you want to replace. Or your machine may be a Mk1, and the part, when it arrives turns out to be for a Mk2A. and so either will not fit
(They upgraded / changed the gears, sizes or threads? May even have inverted things like dovetails)
It might even be a total hybrid, an All Spare Parts, assembled by someone whose only skill is making a good paint job! Maybe misassembled / maladjusted.
A bargain perhaps, if you know what you are doing, but an expensive mistake if you don't.
Restoring an old machine to running order, and using it can be a very satisfying part of the hobby. But not necessarily for the inexperienced, impatient or impecunious.
Fantastic work has been done on old machines. There are folk on the Forum producing excellent work on machines that are a century old. A former working colleague can produce work on a pre 1920 machine that I lack the skill to match.with a 2003 one. But that is my shortcoming!
You might even end up in the Catch 22 situation of needing the machine that is pieces to make the very part that needs replacement!
A friend bought a 80 year old machine. Basically good, but it would not turn parallel. The problem was solved, using my lathe to make repair part.
Having helped lightly repair / restore a few oldies, for friends, I have been fortunate in having my own machines available to make / modify / restore parts. Without such facilities life could have been difficult.
Caveat emptor!
Howard