Hi Mark,
I made the video and have never had this problem with LAW50 gears. They can be a bit notchy when new but wear in after a couple of runs. What shims did you use inside the diff? as these set the backlash in the gears and if too thick then will give you what you describe. There are a couple of options:
1. try thinner shims, the standard ones are 0.15mm so try 2x 0.1mm shims and see if this frees it off
2. take the two larger gears and rub the back of them with some fine sand paper
3. use a second gasket to space the casing (I don't like this method either which is why I don't mention it in the video but others use it effectively)
Hope that helps
