Hey Ol'Smokey,

When I first read the title of your thread I thought you must have been talking about getting arthritis in your hips!
Its fair to say motor cars are a bit like people in that rear ends dont get looked after as well as they should !!

A good indicator is the number of threads where people say how hard it was to remove the diff plug. It must have been stuck a long time!! Maybe from new.
Splines are the least of ones worries, reduced oil volume is likely to reduce lubrication to the pinion & carrier bearings, they will in time let you know.

With most DIY's not having a hoist, its not surprising that rear ends get neglected. You can be sure that there are service tech's that just tick the box without removing the diff plug.
let the truth be known, there would be plenty who only have checked/changed the diff oil because one of the drive shaft boots had to be replaced.
Then there are those on here who will let you know in no uncertain terms when you dont do exactly what the book says.

We should be more concerned if the diff oil started to smell burned at all as this may indicate overheating.

Best of luck with your car !!!!

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving