Update:

I switched to the engine oil to ConocoPhillips Gaurdol 15w40 ECT which has two important characteristics!

ZDDP (zinc) levels of 12,600 ppm (or 0.126)
HTHS rating of 4.4

Thus far the oil has remained the same level, and the engine now purrs! Also used a Napa Gold 1515 oil filter... no oil drops after 300 km thus far!

Thank goodness for realizing the zinc and shear rating were uber important after reading and article talking about using Rotella T 15w40. ConocoPhillips Guardol works like a champ!

Cheers

 

Thanks for reporting back.
I told you your engine was not toast.

 

Spike555

I find that too many times people do not report back and that leaves even more questions, so it is important to follow-up

I was concerned after having spent enough money to buy a newer used Disco II... but I just love the Disco I's R380 manual transmission too much to give it up!

Although the rover is not without its quirks I still love the Disco I. Yesterday the engine decided to keep revving from 1,000 - 1,500 rpm for about 30 minutes, and then went back to normal, and the door lock actuators are a nuisance after I replaced them... still doesn't dissuade me from the Rover

 

Follow-up:

I switched from the ConocoPhillips Gaurdol 15w40 ECT to Shell Rotella 15w40 as over time the ConocoPhillips started to dip low. I believe it is do to the fact that it is a semi-synthetic (roughly 50% synthetic and 50% non-synthetic) and the synthetic was finding its way through.

The Shell has been a fair bit better, perhaps half a litre every 1,500-2,000 km (1,000-1,250 miles).

I am going to switch it up to Kendall GT-1 High Performance 20w50 with added Zinc of 1,200 ppm and a High-Temperature/High-Shear (HT/HS) Viscosity rating of 4.7!

Kendall GT-1 H/P 20w50 also has a pour point of -30º C (-22º F), so it will not adversely affect me in the winter where on rare occasion in Vancouver, B.C., Canada the temperature dips to -12º C to -15º C (10.4º F to 5º F).

That should potentially stop any leaking, or make it almost non existent. From my days working with ConocoPhillips I can get a great deal on the oil at $2.40 (CDN) a litre/quart.

 

I've used the Kendall 20w-50 and have been happy with it. That or the Valvoline VR-1 oil in 20W-50 are my two 3-season oils. I usually switch back to Rotella 15w-40 for the winter though.

 

Follow-up:

The Shell Rotella 15w40 was dipping low a bit, so I switched to Kendall 20w50 GT1 with added ZDDP.

After a long hectic back country trip going 4,700 feet above sea level for most of the trip and about 1,000 km (621 Miles) in 35˚C - 41˚C (95˚F - 105˚F) temperatures, I was only down about a quart of the 20w50. I pushed the engine hard up some steep inclines both highway and off-road, and also noticed that it was having a hard time at those elevations getting up to 90KPh (55Mph).

I have also spotted a potential culprit that might be leading to some oil leakage. I noticed one of the spark plugs is leaking a bit of oil out of its cylinder, and the spark plug seems to have come loose out of its cylinder. I think it is from the bad VSS making the vehicle buck and shudder all the time (especially in the city with shifting gears all the time) unless I am on the highway in 4th or 5th gear.

 

Finally tracked down the oil leak after some searching. It was the oil pressure relief valve o-ring.


The original o-ring was as hard as a rock and 19 years old. I replaced it with a Viton o-ring of the same size. Now, there is no more oil in my parking spot, and the filter is clean with no oil drips hanging off of it.

 

It's such a good feeling once you find an issue that's been haunting you!

 

Yep! I hope that of anyone else has oil loss, they check and replace that o-ring which costs $0.50

I'm also grateful for all of the help from this forum!

 

I don't know where this comes from:
Oil is important, but I think you're attaching more importance than it has. Any of those oils you listed, and a whole lot of others out there that meet the minimum specs should work just fine, including Walmart oil. That whole ZDDP camshaft wearing-out thing was way overblown (low-grade import shafts at the time for one). Glad you got it sorted out though, and thanks for sharing.