Changing differential fluid- mileage or age?
 

Newly acquired 92 300TE 4matic with 33,000 original miles. Deciding whether to replace original-fill fluids in front and rear differentials. Do these fluids deteriorate over time (like brake fluid) or can they remain in the car until the recommended 60K mile replacement?
I realize that it couldn't hurt to do it, but would it hurt not to do it?

You really won't know unless you sample/inspect the oil, which is likely more costly than changing it out.

At 33K the car should have had fluids changed anyway. Since you're a "new" owner, it's the perfect time to refresh ALL the fluids and filters and start keeping good maintenance records.

Differential fluid should be changed every 30,000 miles ... same for transmission fluid.

It's only $10-15 bucks worth of oil--do it anyway.

I figured that's what everyone would say.
By the way, MB specs a special hypoid fluid for the rear differential which runs about $35/liter. Front diff. takes the standard hypoid since it's a non ASR differential.

Change it, I do diffs at 25K like the trans, easier to keep up with at those intervals.

I'd run synthetic fluid in your diff's..be it lubro moly or redline. It's cheaper then the MB bits and I'm sure works just as well if not better.

Keep the fluid in the 4 matic diffs fresh @ all cost... Fluid is MUCH cheaper then new cases.

Jonathan