There is a sequence in the preload adjustment. The worm gear thrust bearing preload is measured 1st with the adjuster plug loose (Drag). The adjuster plug is then tightened to get the preload spec and the the locking nut is torqued down. This step can throw the thrust bearing preload off so you need to be able to hold the adjuster plug still.
The rack and recirculating ball preload is next. A tool is used to hold the recirculating balls withing the rack. The assembly is then slid into the steering box as you turn the worm. If the correct recirculating ball size is selected, only a slight increase is drag will be measured. If there is no increase, choose the next larger size. I install the pitman shaft at this step to prevent the rack from rotating.
Install the pitman shaft cover and perform the final preload steps through the center high point.
I attached a worksheet I use to adjust the preloads. The shop manual steering section 9 goes into more detail. Special beam torque wrenches are used to measure these tiny preloads and you can get by with a digital Mitutoyo micrometer to measure the recirculating ball diameters.
GM recirculating ball inventory is pretty much depleted. eBay, Ali-Express, etc has metric versions that can cheaply make a select kit. I don't know the quality but I was considering trying them for future projects. I think they are used for bicycle rotating assemblies.
In your video, the amount of play doen't appear excessive off center. The center high point is the only spot where you get the greatest preload.
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