The rear main seal is one of those $20 parts that cost over $1000 in labor if you don't DIY.

The list of items to R&R....

Front splash shield
Subframe stiffener plate/swaybar
Center exhaust section
Exhaust heat shields
Driveshafts
TC case/crossmember
Trans wiring harness/linkage
Transmission

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'03 X5 4.4 Sport, last of the M62s (8-03 build date)
I believe in deadication to craftmanship in a world of mediocrity!