PAS reservior on Discovery II

Has just been topped up over the last week with a litre of Transfer box oil of the 75W/90R, API GL5 spec

Don't ask why, it just has

Seems to be working fine but is this going to give me problems

What should I do

Anybody there

I mean am I going to get away with this if I just keep adding in the proper landrover PAS oil Will it mix in with the PAS oil already in the reservoir/system Can the pump handle it will it damage any seals

It's currently losing about a 1/2 liter per three days so it's getting topped up twice a day at the mo with PAS oil. It scheduled to go in for a steering box next week and will get a full PAS oil refresh then.

Question is do I need to move faster or is too late already and a pump as well as a steering box is on the cards

Help