Rear wheel removed, Guzzi on stand: many of us do not need to remove the wheel as stated before, "on stand" is enough. Here's a pic of the grease nipple. Nice pic, thanks, next best thing to me investing in dental mirrors! I should get my fingertips to make sense of it now.
I found a swanky grease gun with flex hose, one handed trigger action, but it's BSP thread which is standard on grease guns here. Probably going to be some grinding of the nose to fit on as it's a porky little thing, might be 3/8 fitting, another possible explanation for the variance of ease getting on.