the questions that immediatesly spring to mind are:-
1) teh E series doesnt have self levellign suspension does it?
2) is there any oil 'forward' of this point
3) whats above this - afaik
theres nothing above it
4) what sort of consistency is it - oil? fuel? whats does it smell like? could be transmission / diff leaking. brake fluid (feels 'dry')
that bolt is just the semi-trailign arm mount bolt - a bolt through the lower arm that holds the wheel in place. there shouldnt be any oil round there.