What Joe said.
The WD in WD-40 stands for water displacement. It isn't a substitute for proper oil. Most of my experience comes from restoring vintage woodworking machines. We don't use a lot of WD-40 or other spray lubes for for that either. If a machine is frozen, it may be of benefit to spray it down and walk away for a couple days to let the WD-40 do it's work but after the machine is freed up it's important to wipe the machine down well and oil it properly. Leaving the spray lube in the machine is just asking every bit of stray dust and lint to collect in your machine. You'll end up with an even bigger mess down the road. Also, I haven't had to deal with this yet but if your machine has plastic parts inside the worst thing you can do is oil them. It's been reported that some types of plastics used in these machines will swell or melt if exposed to oil.
There are also machines out there using cloth belts to drive them and you want to be careful around those as well.
Also, let's face it. If we're playing with these old machines there's a good chance we already have more than one that's running so time spent cleaning and oiling another one really isn't that critical. There's no need to rush it.
Rodney