02 F350 wont start- really need help!

[wolve1060]

Ive got a 2002 f-350 powerstroke. It will start just fine when it is warm out but when it gets cold out it will not start. It will just sit there and turn over acting like it wants to start and have white smoke coming out the exhaust. I took it to the local diesel shop to have them take a look at it and they told me that the oil cooler is leaking and that is what is causing the problem. Its got new injectors, new glow plugs and new glow plug relays in it. He told me it will cost $400 for the repair and parts. What do you guys think? You think that could be the problem and is that a good price? Im supposed to tell him in the morning whether or not to do it so please respond with your comments!