Never had or heard of any experience with it but I would say go for it if you want to. Regarding the X5 gearboxes being prone to problems . . . every other part on the X is prone to problems too. It is a fact that several parts on the X are going to break . . . it's an X5. If you want to go fast in between parts failures and repairs . . . go for it!

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2010 Lexus RX350 still new
2003 BMW X5 3.0i w/sport package w/68K miles. (gone Thank God!)
2002 Dodge Ram 2500 4X4 cummins diesel w/198K miles, custom repo truck
2009 Scion tC w/46K miles
2007 Suzuki SV650 custom streetfighter
2000 Lexus GS400 w/165K miles