I wonder sometimes at all these hard cold start posts.
We were in the teens a few times when I was in OK around thanksgiving, and a night or two here in NC not too long ago, and mine fired right up, no more then ten seconds after the glow light went off(habit from VW diesels, if they don't start with a ten second hold over after the light, there not gonna start).
I think you ought to get your battery load tested(duralast should still be in full replacement warranty i believe) and find someone that can test the amp draw on that starter, I know advance and autozone can with it off the car, can't remember if they can do it on the car, should be able to. If the glow plugs are all at least working, it's spinning over good, and there arent any funky air leak issues, it really ought to fire up well into the teens.
Another thing I think of when I read these posts, if you've got a so-so battery, three full glow cycles is a lot of load to put on the thing and THEN try and make it spin over. You may well be better off with one good glow and a crank with a less-depleted battery.
It just all depends on the motor.
VW diesels in good repair fire up easier and idle better in the cold than the 617 seems to. But...
