The E83 X3 front diff is painful too.

Anyway, at the Front Diff side, 3 potential sources for leak...

- Axle Seal, after 143K miles and millions of revolutions by the
axles, any seal dealing with a rotating shaft will leak...
I will replace the seals.

- Gasket at 2 halves of front diff. Rarely leaks, even if
it leaks, it is a slow leak. Probably can watch.
Btw, do they sell the gasket or you have to make your own?

- The 2 O-rings, I have not heard any complaints in this
forum over the years... probably can watch them.

I am just trying to minimize my work lol...

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1998 E39 528i 5sp MT
2006 E53 X5 3.0 6sp MT