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I assume the R60 is pre 1970.https://vintagebmw.org/forum/viewforum.php?f=7&sid=1eff2e6f8aa117b369f2f18537c5c4acThey should know the answer.In the short term remove the fill bolt and remove some oil to get it just below the fill hole.Check drive shaft oil level.If it is the slow leak it should be good for many miles before oil is pushed out again.Check again when changing engine oil.Heat the housing several hundred degrees (barbecue grille works okay.The fixed axle spacer will slide out of the casting.(So will a few other parts.)This leaves the "hidden" seal exposed for easy removal and replacement.Warm the casting and freeze the spacer and it will drop in.Don