Query from Caterham 7 track-day driver. I have used your MTL gear oil for 3 years in a Caterham 6 speed box with good results and found it far superior to the original Ford red stuff. The gearbox leaks so I use more than I would like. However Caterham are apparently now saying that synthetic oil is NOT recommended and we should use mineral oil EP80 GL4 grade.

This is a regular question. The high street synthetic gear oils are too slippery to let the synchros work properly. In a road family-mobile you will never notice you are getting a slow change, but in a Caterham with a short gear lever you can too easily beat the sychro hub engagement speed and potentially brake synchro rings. The Red Line MTL and MT90 have friction modifiers to allow the proper engagement of the synchromesh - at any speed - but unfortunately this is not a cheap option. Because the Ford oil is bought in VERY cheaply from Texaco (now owned by Shell) it is not friction modified and Comma (owned by Exxon) support the Caterham race series and don't produce a suitable synthetic gear oil, thus it is politically correct to say synthetics are not recommended. To be fair to Ford, Shell and Exxon, for ordinary road cars there is no need for the expense of such a good oil. Caterham are just in the proverbial hard place. If the high street guys produced top spec oils commercially, it would put niche market blenders such as ourselves out of business!