When I've replaced the bushes I dribble some 90 grade down the top gallery before greasing, in the hope that it will get down to the top of the upper bush, (having pre-greased the bushes before refitting). Some Triumphs used gear oil in the lower trunnions - Herald/Spitfire TRs as I recall. All I would be cautious about is that some hypo oils are said to erode yellow metal.
The other unusual thing about the Morgan lower grease nipple is that it enters the stub axle above the lower bush, whereas MG grease nipples go directly into the bush. Obviously the challenge there is that when pressing in a new bush you also have to align the pre-drilled hole with the grease channel. At least with Morgan you don't have to bother with that.
There is also a hydraulic 'lock' effect when you pump the kingpin up and down in the stub, because with the grease nipple removed, grease emerges from the hole, so it seems that with the nipple in place, grease may be forced down the channels in the bushes to some extent.
For a while there was no top nipple in the upper 'lube' bolt, so there must have been some confidence that grease would also be forced up into the upper bush.
