Final drive, cat 955l leak, procedure .

Unless you get lucky and tightening the outer final drive bearings takes care of the leaking your in for a change of final drive seals. A fairly major job requiring hydraulic puller and press equipment.

ok.
I checked the level from the back hole and about halfway through.
We need about 2 liters to fill it.
He loses them all.
I assume the loss is in the upper part.

Are you seeing leakage on the tracks below the final drive hubs?
Oil has to go somewhere. If not leaking external than it is most likely adding to the steering clutch compartment.

Yes gets lost outside ..
you can see the oil marks from the top over the track.
I think I'll leave it all like this.
Could it be a problem?

take the bottom plug out and rinse the case with some diesel or solvent. see how many chunks come out and let us know.

Is the top of the final drive case worn through from the track wearing on it??

take the bottom plug out and rinse the case with some diesel or solvent. see how many chunks come out and let us know.

hi ,What could have happened?

Quite a few things could be the cause of the leak.
A loose outer hub on the sprocket shaft can pop the outer nut off the threads.
Wire could have damaged the seals.
Might just be worn bearings needing adjustment.
Bearings may have collapsed.
Loose sprocket on the splined hub.

First check the the bearing pre load and outer nut.
If that doesnt work, you will have to start stripping.
You need special equipment when it comes to pulling off and pushing on the sprocket.