Yikes, bright grey color, not sure what that means....combination of moisture, acids from combustion, ash+ soot contaminants and the list goes on..

-can you expand on his reasoning Neil ? does he believe OIL never breaks down or wears out etc..not even the additives?
-what about changing the oil filter? is that a waste of time and money as well?

Alkyl Zink was pulled out of automobile motor oil because it fouled Catalytic converters and they failed before the 5 year warranty ran out. Big 3 auto makers forced the change of the api spec. I used to have the documents and back room letters on the subject. Remember in the late 70s when engines started having more failures? I ran diesel spec oil in my entire fleet of 3000 vehicles. 

I don’t know any history on the unit. He just picked it up and its a fully functional machine. Just looking to do some maintenance and fluid changes on it. I had heard that gear oil potentially could cause damage to the Cone seals in the final drives, but not sure on that. It was apparently due to the EP additives in it. 

The saying Ive heard and live by is “oil is cheaper than Iron”.
Better to maintain the lube oils than have Metal parts start failing due to poor lubrication.

wombat i agree oil is cheap parts are not. a friend of the family told me when his dad was a grader operator for the shire council he would always grease it at the end of the day even if it was pouring rain 1 the machine lasts longer and 2 your already dirty so whats a little more grime going to do and bonus you simply simply start the machine in the morning and go to work your not smelling of grease and oil all day.

i think there was a copper bellows type seal used in the final drives in the 1930 1940's era. i guess the ep additives in gl5 could affect them over time.  i also think thhe ep additives have changed a little over time also????

I read somewhere on a gear oil site that the additives in GL5 were modified a little so it wouldn't affect bronze parts