Since i bought a new GK i didn't take a single goal and at today the only 2 goals taken in cl/league were with the old keeper playing. Winning from 5 to 9 - 0 the new keeper didn't score under 7 once.
The GK rating is important from what i noticed until now. If he keeps scoring low, the time you'll face a half decent opponent you'll take goals in due to his poor rating. I advice you to change it asap before you start facing stronger teams. Check back your cup matches and last season's last CL match, and see what he scored.