It should be a regular nipple so normal grease gun head should push on and lock. Only minimal amount not grease though as you may blow the seals otherwise - just one squeeze on my Wanner.
Not sure about M3W but on the four wheelers there are three nipples, located on UJ at each end of propshaft and a sliding joint just behind forward UJ. I think this necessary sliding joint is integral to front UJ on M3W and locates on gearbox output shaft splines forward of the UJ. Worth checking to see if it has a dedicated lube point.
