What is causing diesel fuel to get into my Antifreeze overflow tank? need some advice

I have a 2005 F350 6.0....I went to check my oil the other morning and noticed about an inch of diesel fuel on top of the antifreeze in the resevoir tank. What causes this to happen? I have looked at different discussion forums and seen where someone said in the 7.3 it would be the injector cups. and in another one I seen if it was in the 6.0 that there couldn't be any other thing but if one of my heads were cracked. I called the dealership, and they told me they couldn't tell me anything unless I take it in there and have it checked out. And that the only way to tell if it is the heads is to have them taken off and have em sent out to check.
Man o man, this 6.0 has been nothing but trouble since I bought it. One thing after another has gone wrong with it. The truck I had before was a 7.3 and I tell ya what that is a much better motor my opinion by far.
I have had this truck for less than 7 months and have already sunk more than $7000 in it in repairs.
If anyone has had this problem before and may know what it is I would greatly appreciate some advice, before I have to go and spend out the yang just to find out what the problem is..Thank you