It seems that these hubs use grease rather than oil to reduce the need for regular maintenance (oiling) and make them cleaner as oiled designs aren't totally sealed so leak to a small extent. The downsides of grease are that it can migrate away from areas of load and dry out over time. There's potentially also less natural "flushing" action compared to oil since it all stays inside the hub and will retain contamination. It also needs to be applied directly to components, meaning more disassembly if re-lubing.
So, oil requires frequent if minmal attention and is a bit less convient but should last forever. If it did need attention, this could probably be achieved by flushing and re-lubing without disassembly. Grease remains maintenance-free for a longer period of time, but will ultimately require stripping; cleaning and re-greasing.
Thixotropic or semi-fluid grease appears to mitigate these issues somewhat as it becomes less viscous under load, meaning potentially better coverage and distribution in use, but less chance of migration and leakage when static.
There's a thread on the CUK forum in which a landrover swivel pin grease is recommended. Its also suggested that its viscosity can further be modified by adding gear oil (presumably mineral-based). Another suggestion is thinning out CV joint grease (which contains a lot of moly) with gear oil, but this probably doesn't display such desirable thixotropic properties.
I like moly as it's great under high loads (hence the CV joint application), although it doesn't seem that prevalent in automotive gearbox lubrication. I did find a Molykote product for (presumably non-automotive) gearboxes which contains moly. It's possible / likely that the Landrover stuff mentioned above might also (a video containing some seems to back this up given it's colour).
What's on the end of my gear indicator chain is a uniform dark grey and somewhere between CV joint grease and oil in viscosity.. so could well already be something like those described above. It doesn't look visibly contaminated and I can't really feel any roughness between my fingers..
While I'm wary of "sealed" / claimed "low maintenance" products it seems that what's in there should legitimately last a decent amount of time, and I can' add the odd drop of mineral oil down the axle periodically to ensure it doesn't become too thick.
Further down the line / when time allows / when I have the spuds to sufficiently disassemble it, I can look to strip, clean and re-lube the hub - for which I'll apparently need a Sturmey Archer HTR 145 Classic Ball Ring Spanner in addition to some cone spanners.
