[DCinVA]

Since the compression is 175 across all 6 cylinders, I would think the results of the leak-down test are suspicious. It is important to follow the proper procedure when doing the leak-down test on a flat 6. Basically the procedure is one cylinder at a time. I.E. rotate the crank to the proper position, remove the plug, do the test, reinstall plug. Follow those same steps for each remaining cylinder.

I have heard it said that when you pull a plug, sometimes a bit of carbon from the head is dislodged and drops into the cylinder. If you pull all the plugs at the same time, dislodging bits of carbon into cylinders, and then turn the engine over, those bits of carbon would be pushed around in the cylinder, and hence could become lodged between a valve and its seat as it opens and closes. If you follow the procedure outlined above, even if a bit of carbon falls into the cylinder when you remove the plug, the valves are closed, you do not rotate the engine, so there is no possibility of lodging carbon between the valve and the seat, which ruins the result of your test.

Having said all that, I would still be suspect of the car, and would probably pass on it.