BMW E46, E60, E81, E82, E83, E84, E85, E87, E88, E90, E91, E92, E93 Vacuum pump O ring replacement.
The vacuum pump was weeping oil from the pump O ring, so a seal set(2 O rings) was ordered, part number 11668626471, this kit fits many BMW models, as shown here. RealOEM.com * Part Cross-reference
The pump itself is held on by three 10mm headed bolts, you'll need to remove the pollen filter housing(s), and all top bulkhead plastic covers, strut bars and top engine covers to get anywhere near the pump. Then you can unbolt the pump from the head and remove the vacuum pipe from the pump.
New seal kit.
Once the pump is removed you'll have this.
The pump cover is held down by seven T25 torx screws, once removed you'll find the old O ring has flattened down, causing it to leak oil.
This is the new O ring fitted, you can see the 2 ridges on the seal if you look closely.
Now you can re-secure the pump cover with the 7 X T25s, replace the smaller O ring that stops oil leaking from the cylinder head past the pump, and refit the pump.
Hope that makes things a bit clearer for anyone attempting the job.