Hi Tony
50 years of lubrication experience is not easy to summarise in a short post unfortunately.
I spent much of my career for better or worse trying to solve lubrication problems in far more exotic and much much much more expensive machinery than Lotus front trunnions ( think a hundred million dollar piece of machinery and you are getting close) but the principles are the same
I also been fortunate to have learnt from some of the best machinery engineers in the world during my career and I try to apply that learning to my love of Elans
So in summary about the challenges of "Lubrication of the Elan ( Triumph ) front trunnion"
1. The trunnion is a low speed brass on steel sliding surface. Brass on steel is a good combination for sliding service at any speed but works especially well at low speed and relatively low surface contact loads as present in the trunnion so the design and materials selection is basically OK. The design detail with the segmented thread in the trunnion is also good as it ensures a good lubricant supply to the sliding surfaces ( especially if you use grease ... surprise!)
2. Both oil and grease are OK for this low speed service if you can keep it in contact with the sliding surfaces and un-contaminated. At higher speed such as in a gear box where you have brass and steel sliding services in the shift forks and synchros, oil is more desirable as well as the fact that it is needed by the rest of the high speed gear box components versus grease. In things like wheel bearings at lower speed you can use grease as its suitable at these speeds and retaining oil in them is much more complex which is why all your wheel bearings use grease. At lower speeds still, like in the trunnions, grease is the obvious choice and was used for many years by many car makers for lubrication of chassis suspension components as it provided lubrication and stayed in place where tight sealing was not easily possible or needed if you used grease, like leaf spring suspensions.
3. So why did Triumph specify oil for the trunnions???? While I am no expert in the history of grease development over the years and cant read the minds of the Triumph engineers back in the 50's, I believe it was chosen as it was reasonably practicable to get a half decent seal with the vertical arrangement of the trunnion with a top rubber seal and due to the poor characteristics of greases back then in the 1950's especially with the grease caking and setting solid due to the soaps or clay based oil carriers used in greases then, so using oil was desirable versus grease.
4. The problem with oil is that the top seal is poor and water gets in and sinks down through the total depth of the trunnion causing corrosion of the steel. The pressed / peened in bottom plate on the trunnion can also leak leading to loss of all the oil. Also pumping in new oil is not easy through a grease fitting with a grease pump. If they really thought oil was the right solution they should have designed a proper oiling system ... but the accountants probably thought that would cost to much
5. So why not use a modern GL-2 EP lithium soap grease I asked myself in 1974 when I first got my Elan. The modern lithium soap resists water and prevents it getting into the trunnion and contaminating the lubrication. The modern EP grease is perfectly adequate for lubrication at the speeds encountered in turning the steering. Grease will not leak out from the bottom plate. Pumping grease in and displacing all the old grease with new grease is easy. So far my answer has been yes and that's the right way to go and I have done it since then as have many others with no issue.
6. People have successfully used oil per the Triumph recommendation and I am sure it has worked for them. People have made up semi fluid greases and I am sure it has worked for them. I don't say "don't use oil" All I say is technically a modern grease of the right specification ( i.e. lithium soap, Gl-2 , EP grease) is the better solution considering all the issues. Also don't mix greases so if using grease, use the same type and brand or clean out the trunnions and start with a new grease as the different grease soaps can react if you mix types and this can lead to problems
It a seemingly very small and seemingly simple issue but like most engineering problems there is a lot of breadth and depth of questions to ask and answer in coming up with a solution. I try to ask myself the questions before trying to find the answers
cheers
Rohan