Try using a small oil pump to fill next time , amlube or tomthumb they make getting it into the fill plug a bit less painful, the side with the metal on the plug I would drop the oil again after some use and see how much metal it has on it , might give you some insight on the health of the inside, they are rather expensive to rebuild, by comparison oil is cheap.
I do keep meaning to get a oil pump for filling gearboxes thanks for the advice. I was planning on doing that bed again just not looking forward to taking that bung out again 🥴
