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Assembly
Short answer, no. Long answer, it won’t hurt until you need to replace or remove the ejector. On my AR-9 designs the ejector is 3D printed, it presses into a pocket on the lower. This may be concerning to some users, as it appears to only be a friction fit holding the part in. However, if you look closely you will see that the upper receiver holds down the edge of the ejector when the upper is installed, this locks the ejector in place so that it can not escape. I do not recommend glue.
I stopped using washers on the bushing installation tools some time ago. This was because the benefit was not worth the trouble. The washer is hard to install, easy to lose, and without it the tool does no significant damage to the surface of the lower. So no more washer!