My entire year got HP Zbooks and they have had pretty high failure rates and replacements have taken over a year in some cases. The fastest replacement I know of was 6 months...
Zbook 17's are awful machines. The Zbook 17 G1 and G2 at work have both died. The Zbook 17 G2 had it's GPU replaced 4 times, 3 times with faulty GPUs. The Zbook 17 G1 we have given up on, Shame because it was VERY expensive.