Regarding the switch in the G810, it's a Romer-G switch. Only Logitech uses those. Forget the O-ring mods. Apparently they aren't compatible with the Romer-G switches at all.
Regarding the MX Silent switches:
The MX Silent is used in this keyboard, for one:
https://www.newegg.com/global/uk/Product/Product.aspx?Item=N82E16823816065
There are four MX Silent models: the Red, Black, and the RGB versions of the same. The MX Silent Black is not the same as the MX Black. It uses the same internals, but also has a damping treatment added to make it quieter. It's the same deal with the other models. They take a switch, apply damping, and call it a Silent switch.