For those who have audio before webcam sync issues, increase the stream fps to 31 in settings > video tab. This will stop it going out of sync. (It will allow the webcam to slowly catch up to real time again because it will be capturing at 1fps slower) Equally you could set your webcam FPS to 29 in OBS as well, and run the stream at 30fps, although this will cause some occasional micro stutter on the webcam. As long as the webcam is 1fps slower than the stream it will stay synced basically.
For those who have webcam before audio sync issues, try increasing the cpu priority to above normal or high on both your webcam software and also OBS.
(this may have already been mentioned but i've spent some time tinkering so figured i'd post it just incase it's not known)