Get it fixed. Your fresh air pickup is usually under the cowling below the windshield, partially under the hood. If the hot side of the turbo is cracked it can indeed release carbon monoxide and whatever else is in exhaust and that can make its way into the cabin. Your cabin air filter won’t do anything for carbon monoxide either.

Get it fixed, or you risk sleepytime while driving, which usually means you’re going to have a bad time.

Sounds like a bad window regulator

If you have been driving around with a failed head gasket for 6 months, it’s likely that you have destroyed the engine and the whole thing will need to be replaced.