Thank you for the feed back guys.
I was wrong about the thickness, its 3/4 oz not 5/6oz. I shall take everything you said on board, I am a little nervous about cutting deeper though.
The tools aren't the best quality, the swivel blade needed a lot of work until it felt nice going through the leather. Mostly though the oil marks are down to operater error.
Here's another piece I did before I read the replies