To OP, unless you're willing to go thru he-l to prove a case, reporting harrassment before you leave will get you nowhere. HR are shills for management. I agree with your judgement - find a new gig and report it on the way out. If the complaints mount up, eventually said manager will get let go. These folks saying to report it immediately are extremely naive - nothing will come of it immediately but harsh repercussions. If you believe HR is 'on your side' then I got a bridge in the Mohabi that I'll sell you.
I mean if it's causing you mental hardship & it will help your mental well being to confront the sit-e-ation - by all means, report it. But I've had no luck expressing hardships to HR - they're there to hire and fire. I'm giving you the harsh low-down after 20+ years in the corporate world. I've seen incompetent folks stay in a large org for years. If you're a good corp citizen and give an ounce of value, you'd be surprised how long you might stay in a company. There's a huge list of infractions required to fire someone for misconduct. He-l - I've been outright belligerent to people and been retained b/c of my work ethic.
But yeah - i hear ya, the devil you know and all that. I understand the spirit of your post - hang in there buddy. What your going thru is a nightmare - so many posts of ppl who left and say 'things are so much better' - you offer the counterpoint.