My '01 5.9 D is approaching 128,000 without a fluid change in either the tranny or differential. So far I've been fortunate, it engages and shifts fine. No slips or leaks (maybe a slight leak around the diff cover).

Will changing the fluids and filter at this point accelerate wear? If the consensus is to change the fluids, and brand/type in particular?

It's had any easy life with regular maintenance, well except the tranny and diff, and I'd like to keep it on the road for many years to come.

 

No.

Get them serviced and ensure they use ATF+4 ONLY in the trans. ....Yes stand over them and don't let them install multi-vehicle ATF transmission fluid.

As for the diff's. If you have a limited slip diff then you need to use Friction Modifier (at least 5oz) per service manual. I would run at least 7oz. I prefer Mobil One Fully Synthetic 75W-90 hypoid rated gear oil.

 

128k with no service?

YES get it serviced ASAP.

NO don't blame the service on premature failure of your parts thereafter. You have already most certainly confirmed that will be the case in soon to short order.

Two words for you, "Scheduled Maintenance"

IndyDurango