I looked up the part number on the probe, it LJ12A3-4-Z/BY. It's a PNP, 6-36VDC 4mm Detecting Distance NO Inductive Proximity Switch. I also tested my probe and the LED works correctly, but the output with a 12V supply is 6V, and when triggered is 4V, so I think this is also bad. They were $5 on Amazon so I ordered two.
I like the diode with no MOSFET, if I were not getting a replacement board, this looks like the best solution I have seen. The MOSFET could be removed from the board, or I could reassign an open pin from the Extension Pin Header. I would need to re-compile and flash the board. I have poked around in the source code and found how to change the pin numbers, but I don't think I'm quite ready to go there just yet.
I can print just fine with a level bed, and no Z stop. To be honest, I have made the best prints since the Z Probe went out. I have only been printing for a few weeks, so that may not be saying much:) I think for now, if Printrbot follows through and replaces my board, I will run it stock, but with added grounding. Grounding the probe case to give any static discharge a path to ground, and a choke on the Z Probe wires to discourage any static discharge (or induced current) from traveling down the probe wires can't hurt. If the MOSFET get's taken out again, I will make it work another way.
Thanks for all the discussion, this has been interesting and information I can use!