Oil....an ever re-occurring subject, and as they say, "a little knowledge is a dangerous thing!"
I have a long standing friend who happens also to be a classic car enthusiast. After graduating he started out analysing the oil in open cast mine trucks with a view to preventative maintenance - really high tech stuff but when one considers the sums of money involved in those mines it becomes understandable. His career brought him to the UK and he has become a world authority on engine oils, now working freelance and travelling all over the world to lead lectures and seminars.
He wrote this:
http://www.mginfo.co.uk/upgrades4mgs/Fl ... luids.html
....and the section referring to ZDDP:
http://www.mginfo.co.uk/upgrades4mgs/Fl ... tives.html
I also happen to have another friend who works in Castrol's development labs in Pangbourne as an oil chemist. Very interesting what she told me about the original Castrol RS 10W-60; this was a fully synthetic oil developed specifically for the A/A+ Series engines of racing Minis! Other spec bands of Castrol RS (0W & 5W -30) have since been released and the RS branding has been replaced by Edge in response to BMW's wishes but the 10W-60 is still available. My A-Series 1380cc block with Stage IV head has now completed 70,000 miles all with the 10W-60 (apart from 500 running in miles) and the effect of the oil is staggering.
In the Triumph, on the advice of both of these friends, I use Castrol Magnatec 10W-40 (This is semi-synthetic).....of course an engine will run on any cheapo oil; you'll only ever see the results of top quality oils retrospectively on high mileage cars.....my cars are driven, and that's why I never think twice about paying the extra for the best oil I can lay my hands on!