Best penetrating oil?

[Bilgediver]

GT 85. works for me, seems thinner than WD 40 so penetrates well. Asda sell it
GT-85 Spray

On the subject of ships engines I'm sitting not 8ft above a 3 cyl. Crossley at the moment.....Its only a baby but it would
scare the average yachtie......

If the bottom end bolt spanners are less than 4" AF then it is definitely a baby.