One other thing about the 6.0 PSD - RUN it every time you use it. Spin up that turbo and make it work, It's designed for that. Cool it down for a couple of minutes before you turnoff the engine.
Since I started to follow the suggestion above, my 6.0psd has been trouble free.
The theory is pretty simple. Carbon buildup anywhere in the engine will cause problems. Run it hard frequently to get any accumulated crud out, in addition to keeping the fluids clean.
I'm at 90k and have had zero trouble except for a clogged EGT valve within the first 20k miles before I made it a habit to run the motor hard regularly. Despite the bad rep, my 6.0psd has been by far the most reliable motor I've ever owned.
Only mod on mine is a 4" exhaust, and I'd probably have just left it stock if I were doing things over from scratch.
Also, I've had a drop of oil on the bell housing from day one. It very rarely leaves a spot on the ground, and if so, it is only one or two drops max. The level on the dipstick never changes. Given all that is involved with replacing the bed plate seal, etc.......I've decided to just live with a perpetual drop of oil on the bell housing.