Au contraire - do NOT stare at the A/H. These things occasionally get very slight leans themselves, particularly old vacuum-driven jobbies. Even electric ones will sometimes have slight bank errors but not show any flags. So...keep your scan going. If the A/H shows dead level and the heading is drifting slowly, the A/H is probably guilty as charged.
The leans eventually go away with exposure to I.F. in real IMC (as opposed to just pretending under a baseball cap) so seek out cloud with a reasonably high base and just do it for a while. Assuming you have the rating, of course.