I installed zerk grease fittings about 1/2 way down each axis.
The machine is infrequently used (every few days) so I just lube it at the start of each job.
The "grease gun" for it is filled with a synthetic oil mixed with PTFE and MSO2 additive. (www.fluoromoly.com)
May be a bad idea, but it works very well on my mill.