I have a sense that you haven't done this type of work before. Perhaps you could ask a friend or or acquaintance with technical training to drop over?

The problem with using a press is that you don't get any feedback. I haven't done this on a BMW but it looks just like many other vehicles. Install it like any other similar seal. To the same depth as the old one.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue