I see that I am reviving an old thread here - but there is a new option out there besides just "capping off" your egr cooler.
In my repair shop, we had numerous clients that came in with leaking 6.0L egr coolers. We found that doing all the repair work that Ford recommended seemed to make them last a bit longer than before, but still didn't make the truck as reliable as it should have. We checked into the problem and found an "EGR COOLER UPGRADE KIT". You can google it and find it yourself, as well.
Seems that the manufacturers of this awesome new cooler remove the silver-soldered interior and replace it with a well constructed stainless steel interior. It prohibits the solder from melting (its now welded) and the design does not allow for flashing boiling of the coolant. If you want to learn more about this you can here: Leidenfrost effect - Wikipedia, the free encyclopedia
We have purchased a number of these coolers and our customers (and their 6.0's) LOVE them. We give all our customers the option of choosing between replacing their old EGR with the old, Ford style or the new upgrade and they ALWAYS choose the upgrade. They are working well and lasting the way the EGR cooler is supposed to.
Another advantage: it maintains the vehicle the way its supposed to be. You don't have to have an SCT tuner to work around them - just put it in. The best part? If you do have an SCT tuner, it works with that as well! Its the best of both worlds!
Another advantage: does not void state and federal emissions laws.
Just google "egr cooler upgrade kit" and you will find what I found.