Same here, I am using the standard threaded rod and the brass long nut from ebay, working great so far.
If the rod is worn, replace that as well as fitting the brass long nut or it will chew the new nut pretty quickly.
I use 3-in-1 oil on my rod.
Another RS Ormerod Mk1 meets the world
Retired now but I used to make....
CNC Machined Mk1 aluminium bed support plates for the Ormerod
CNC machined X-plates and ribs for Mk1 & Mk2 Ormerods
CNC machined bed support arms for the Mk2 Ormerod.
Dual Hot-End heatsink blocks.