Hydraquadder Oil

[Mechanic]

I am refurbishing a model 78 Linotype equipped with a Hydraquadder. A control  spindle, carrying o-rings, slides back and forth in a cylinder. It is critical that the hydraulic oil does not effect these rings in anyway. I believe the hydraulic oil used by Linotype was manufactured by Caltex. I have a Mergenthaler Hydraquadder maintenance manual.  Their part number for the oil was X-1870.

Mergenthaler warn against using any oil other than the oil they supply, as incorrect oil can swell the o-rings causing the control spindle to lock up. I know this for a fact as Merg themselves unintentionally supplied the incorrect oil. Together with other service reps I spent a lot of time stripping Hydraquadders and replacing the o-rings and oil.

I've contacted Caltex but they were unable to do more than guess, as they need a lot more details such as the composition of the o-rings,  the oil viscosity etc.

The quadder is working but the oil will need to be topped up and I will need the right oil. If anyone has knowledge as to the correct oil to use I would appreciate the information