There is absolutely nothing wrong with the axle spline root. The axle splines are rolled not cut, this is the case with anything "modern". What you are seeing is displaced metal from manufacture.

Moving in a CCW rotation, there is a slight line at the spline tips but nothing even close to being a failure point.

Our guy needs to take the diff completely apart, the failure should be obvious. I'm expecting a failed side gear on the free spinning side and chunks of material jammed between the side gear and spider gear on the powering side.

Do what ever it takes to get call out 72 and 60 out of the way. After that remove the left side cover and the "differential" proper ( right hand side of call out 4 ) will fall out of the housing call out 1. There is no need to remove the 8 bolts holding the ring gear on.

Whenever you determine what parts are broken! The determining factor to repair / replace is locating parts.

When the cost / availability of repair parts outstrips the cost of a used unit. At that point, if you need non final drive ( ring and pinion / diff housing it bolts to ) specific parts, your universe of parts has expanded as generally you can use parts from another ratio.

At minimum, a diff should be able to take 10 minutes to look at cleaned parts and tell you what is broken. If you are able to source all the parts and specs then, the diff shop should be able to fix this. The limiting factor is ring and pinion replacement as it takes special tools to set pinion depth properly. Generally, one can change bearings without affecting this. Diff bearing preload / R & P backlash is set by turning the bearing adjusters making it super easy.

In reality, this diff isn't much different than a 80's Ford 4 WD truck with "Twin I beam " front suspension.

Thanks you for your continued input here.

I've got plenty of extension bar (24" + 9"); but I am having troubles getting a socket in and through the center hole of the Universal joint (#70) to get at that Bolt (#72). Had a ton more chores, but still working on this. Thanks

Does anyone know how Mercedes advised that the flex-joint (#60) be removed from the axle tube? Is there a separate service manual for the differential? Is it somewhere on the web in pdf? My cursory look was fruitless.

I have the Factory Service Manual (Workshop Manual Passenger Car Models 1959) and I can not find any information about servicing the differential. Group 35 Rear Axle has axle and drive pinion info; but nothing about the internals of the differential.

__________________
Currently enjoying:
1967 250S - all manual with 4-spd on floor-- my Nifty 250

Does your socket fit inside call out 65 ? ( RE where the right axle spline engages )

If not, remove internal snap ring 67 , washer 66 and 65 should pull out. I do agree that 65 could have split causing loss of drive but the right drive axle is undamaged and can be reused.

Hi All, just a quick note about how this has ended. Thanks to you all for your input and patience on this project.

I was able to get a whole replacement differential/rear end unit from the folks at Silver Star Motors here in Oakland. I knew that something was amiss in the gears because I could no longer get power to drive the left-hand axle as I had done in Post 11. And though I could gear replacement internals, the time of tearing down the bad and the cost and time of assembling the new was too much. Star Motors was able to do the remove and replace, including some new rubber mounts and bushings for about 8hrs. The replacement gear ratio is still 4.08, so I''ll just have to keep the radio volume up when I'm on the highway.

Now for an engine tune-up (post second cylinder hear repair). Hopefully the car car complete it's 50th year in one piece.

Thanks again, and go enjoy the holiday weekend.

__________________
Currently enjoying:
1967 250S - all manual with 4-spd on floor-- my Nifty 250