I believe the OP is requesting information about the 6.4 psd, but since one person has chimed in about the 6.7 psd and others about other makes I would like to add my experience into the mix.
I own a '12 Super Duty with a 6.7 psd and next week will be one year of ownership. During this past year I put on ~ 24k miles and I have not had one single issue. The truck has performed flawless.
My driving patterns consists of a daily city driver, towing the camper and boat quite frequently while returning outstanding fuel economy unloaded/loaded, delivering some serious performance.
About the 6.4 psd I've never owned one personnly, but a guy at work has a 09 with ~ 180k miles. He mostly drives highway miles and that's what the 6.4 with the first generation DPF prefers and his only shop visit was to replace a idler pully and new shocks this past year. The Ford 6.4 is not your city driver type of truck and it needs to be worked to keep the emissions system in check. Checking the fluids routenly will prevent any of the catastrophic failures like reported here also.
Unless the Ford comes at a great price I would pass on it along with the Cummins 6.7 (07-12) and look for a Chevy Duramax, but again it would have to be at a great price as well. And keep in mind any of these first generation emission diesel equiped trucks will develop issues if now worked hard.
Good luck...