How new is the starter? Is it whirring or actually clunking (for want of a better term where the gear is thrown accross)

Might be worth taking it out and testing it with some jump leads and a battery.

Not going to teach you to suck eggs on tracing a current drain. But I would have thought even a small ish one would only make the starter lazy not actually turn

EDIT : Stretch might be on to something with that