You can have mentors that help you through a particular period; they might be incredible specialists in one area rather than, for example, a company director.
Mentoring can be deep, almost like therapy.
It can be about your career and your life, and sometimes you just need it for three months or so. However, you need to make time to do it by getting away from the demands of your day.
I find it very useful to have mentors that aren't in the same sector as me. I think you should be open about it - sometimes people think they have to keep it a secret, especially when they get to a senior position.
Some see having a mentor as a sign of weakness, but I think it's a sign of strength. You can't possibly know everything, and seeking out advice and support is important.