Tom:
Spirax is semi synthetic, so I won't. We have full synthetic Mobil at work as well as full synthetic transmission lube. Eaton Fuller factory fills all Road ranger transmissions with synthetic now and has no change interval. The fill is for the life of the tranny and/or until rebuild. Same goes for the final drives. No change indicated unless rebuilt.
We are using extended life antifreeze in all our trucks as well. 5 years between changes but still replenishing the additive package when needed. Additive package depletion is checked by relative Ph.
I see the R3 is a linered engine but, I can't tell from the shop manual if the liners are wet or dry. I presume they are dry as Triumph calls for normal ethylene glycol antifreeze with no additive package other than the normal anti-corrosion inhibitors. If it was wet linered, I believe Triumph would call for an anti-cavatation additive such as potassium permagnate or DCA4. I also see that they prefer a low silicate formula but that's because of the non ferrous metals in the cooling system.
The linered engine is interesting. Linered engines, especially wet liner's are able to transfer heat more readily than a parent bore or a straight bored block and are easier to rebuild too. By interesting, I mean that the engine is linered but the head is a throw away item with no cam bearings and cast in guides. Other than production considerations, I can't understand why the head is a scrapper and the block isn't. I'd really dread loosing the oil pump. No pressure would euchre the head in seconds under load.