Start with a new OE BMW gas cap.

The original poster's X5 was hit in the rear so who knows with was crushed, broken, and or leaking pressure in all those lines.

I am sure the body shop is now on a "not my list of repairs" process excuse.
The testing is not complicated. Somewhere out there is a repair tree test procedure that shows, what should the Neg pressure be at the pump, at the separator, etc. The question I asked in a earlier posting was does the diagnostic software, people have been buying in the aftermarket, have the "test evap system" procedure or any of the self tests?

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2005 X5 4.8IS
The Blue ones are always FASTER....

Current Garage:
2005 X5 4.8is
2002 M5 TiSilver
2003 525iT
1998 528i
Former Garage Stable Highlights
2004 325XiT Sport
1973 De Tomaso Pantera, L Model
1970 Dodge Challenger T/A 4 sp Alpine White
1970 Dodge Challenger T/A 4 sp GoManGo Green
1971 Dart Sport, “Dart Light” package
1969 Road Runner 383
1968 Ply Barracuda 340S FB Sea-foam Green