I know it's been a while since I have chimed in, but I finally have a moment to offer my ultimate experience with this truck, and ticking issues. I think for the most part, it's good info. I won't be offended if you pay attention, try to remedy like me, or say hog wash! I did ultimately drive my Disco from Pittsburgh to Williston, North Dakota. When I got to Denver, I had my oil changed at a Grease Monkey. I asked them to put the Rotella in. they did. I asked them to install the big Purolator filter, Ref: "End All To Stupid Oil Questions."

After a day of driving, the car started to Rick again, louder. I almost had a seizure at this point. I decided, whatever the case, now that it was Rotella in the system, and the new pump was on there, the Lucus is the only thing that is not present. I went under my car to drain off a quart of oil and add the Lucus, against recomendation here. Sorry, a ticking motor just freaks me the F out! anyway, when I got under the engine, I looked at this little white oil filter. Not what I showed the guy at Grease Monkey, and specifically asked be installed. I about blew a blood vessel! I went back, had a blow out with the bone head, left, Went to NAPA and bought the correct filter. This is hugely important, because it is the size of this filter, the pressure, and some valve, or something that keeps the oil up in the engine ( the best of what I can gather from sources) I put the Rotella back in, but added that quart of Lucus to be sure. I drove from Denver to ND without a tick and have not had one to this day!

Now that I am here though, for my next oil change, I will get the big Purolator filter, the Rotella, and will skip the Lucus, now that I am in a more controlled environment.

Side Note: When I had the Truck worked on in Denver, because the steering pump that had gone bad in MO, was defective, the warranty on the pump installed by Woodys kicked in, and I was not charged for additional work. AWESOME! I also was told by the Denver boys, MY PROBLEM was/is not a slipped Sleve. It has something to do with the cylinder heads warping in this particular year. Apparently it's common, and it allows for combustion to escape, but the truck can be driven "for thousands of years." before needing to have the engine replaced. Apparently on the ticking scale, I was at about a three.

 

This answer by the "Denver Boys" does not make sense.
Warped head or heads will cause an HG leak.
HG leak will be pressure in the cooling system, coolant into the oil, coolant out the manifolds.
But - NOT a tick.

Year 2003 seems to have porous cylinder walls and some VIN's have bad timing cover which does not align and causes stress on the oil pump gears causing them to shatter.

Year 2004 - some blocks seem to be porous.

Using Rotella oil is a good thing.
Using the correct oil filter will give you more flow and hopefully better pressure.

Best of luck to you..