Is this what will fit in the end of the chain oil gallery on an MS 230 chain saw? Just by the side of the muffler. There is just a hole in mine, must have come out and leaking oil.

This is a known fault with these machines and the plastic insert that is normally in that hole falls out over time. The grub screw you were originally looking at (0000 953 1001) would be fine for fixing this and people tend to super glue them into place.