When I first went lathe shopping years ago, I noticed a number of lathes whose bed ways had spans that were deeply grooved and worn. That is usually caused by poor lubrication, cleaning, and general mantenance combined with machining something abrasive like iron castings, or from using a toolpost grinder without protecting the beds. Such machines have to be rebuilt, and it is a lot of trouble.
A friend and I used to repair machine tools when engineering work was slow, and some are worth saving and some are not. Twenty-five years ago I repaired a couple of 1943 Warner-Swayze 42" turret lathes, and every replacement part was still available. I actually corrected the bed wear by scraping for the better part of a month. Not something I would look forward to doing now. Nowadays, the machine goes to an outfit with a massive precision surface grinder.
I mention all that only because, if you have unlimited time on your hands, including time to learn and practice some skill at scraping, you can actually rejuvinate most old machines. The advantage is the old iron, having been well-aged, and assuming it hasn't been dropped, cracked or badly twisted at some point, is extremely stable. Once repaired and properly figured, it will likely stay that way almost indefinitely with proper lubrication and maintenance and precautions with anything abrasive.
One problem home machines have is they often will be used in spurts, then sit idle for long periods. They need to be operated periodically to keep lubricants distributed. And don't skimp on way oil. Get a 5 gallon tub of Mobile Vactra #2 for a bench size lathe and use it liberally on the ways and in the gear boxes. Recoat the ways at least once a month when the machine is idle. Get a proper spindle oil, like Mobile DTE light. Change it once a year even if you didn't use the machinery much during that time. Turn the machine on and operate the feeds for a minute at least once a month when the machine is idle.