--I think it comes down to a choice of 'living' or 'dead' history;
i.e. if you intend to keep using the machines it's OK to remove the rust,
pound out the dings, re-babbit the bearings, replace the belts, etc; i.e.
address all the issues that would affect accuracy and leave it at that. If
you intend to sell it you wipe off the dust and that's that.

--
"Steamboat Ed" Haas : California: "The crap magnet
Hacking the Trailing Edge! : in America's crankcase".
http://www.nmpproducts.com/intro.htm
---Decks a-wash in a sea of words---