Most of the printers use square linear rail like Hiwin, THK and similar. Most if not all the information above is not correct.
Basically to understand how the rails have to be lubricated is RTFM.
Here is a
link to a Hiwin lubrication manual
IIn short - Never use WD40, Lubricants containing MoS2 or graphite must not be used.
Rails could be oil or grease lubricated and probably most printers will use grease, as oil usually is used in a CNC machine where speeds matter and there is an oil feeding system. Once the carriage is loaded with grease, it would take quite long time to need again grease. In fact i know of some printers that probably have carriages with additional lubrication as per manual it says never to be lubricated.
The manual says:
"Grease lubrication . For grease lubrication, we recommend greases in accordance with DIN 51825 of consistency class NLGI 2 as specified by DIN 51818. For normal loads, standard greases with the designation " – K1K“ are sufficient"
In other words any normal lithium grease not loaded with particles will be alright
If you don't have a grease gun and don't know how to do it, use a sponge and from time to time grease VERY LIGHTLY the rails. Carriages have lips similar to head cleaning vipers so all excessive grease will be wiped and eventually fall on top of the print, that's why no excess is good.
That's it. And if you have time to fiddle and read the Hiwin manual, then FYI the printer applications are probably Low Speed and Very Light Preload, so you figure from there what is needed.
Hope that clears once and for all the rails lubrication.