The Z4 had the same HPFP issues until 2010. The dealer will have the vehicle repair history and can tell you if the the HPFP has been replaced. If it has, find out the part number of the pump because several earlier attempts to correct the problem didn't work because the new pump was still not good. The latest version is good and you can find that part number by going to www.realoem.com and drilling down to the part. Compare the part numbers.
No other significant issues with the car.
2006 525 xi, Orient Blue Metallic, Beige leather, Dark Poplar trim, Premium Package, Cold Weather Package
2012 Z4 35i, ED 2/24/12, Melbourne Red Metallic, Black leather, 6 MT, ///
M Sport, Premium Package, Premium Sound Package, Cold Weather Package, Nav, Comfort Access, LED Angel Eyes, BMWPedals pedal covers, stubby antenna, Luxon strut bar, CF engine cover, LCI side marker, powder coated calipers, Extra Enjoyment Package