Dont know whether Harrison made that Boxford or not but a recommended oil is ATF in the head.
When i get the air powered grease gun out i fill it with old fully synth Castrol Edge motor oil 0W/40W with additives in the nipples, amasing what up to 6000 psi will clear out. Normally dont bother just use the coolant as it evaporates and leaves an oil residue.