Now as you have all been on the edge of your seats on tenterhooks, here is the denouement

As you can see, I placed the obdurate grease nipple in a holder and drilled out a countersink to suit – a new 11/64"

The nipple was reinstalled (2BA) and given a pump and the oil duly emerged from the shaft as expected, only a trivial amount leaked from the gun point
So there is my take on a nasty problem and the grease nipple will no doubt seal on a grease gun
Ive had a few good tips from this board so its good to return – my oil gun tip