Just to be clear in the second video the right rear shock has come undone and so there is 0 damping. The oscillation in that video is different from the original.
https://www.youtube.com/watch?v=CwTlvqOtRa8&app=desktopIn this video go to minute 24; when I come past in this one you can see there is nothing wacky going on. I believe this is before I installed the H190, I initially found and fixed end play in the axles on the H190 which really tamed the car but obviously it still moves around.
I'm planning on replacing the shocks but I'm not convinced they are the problem . From inside the car it doesn't feel like a dead shock(s).
The other issue is most 1200 racers are either not driving it as aggressively as I do or they installed a panhard or watts link at the same time they started running race compound tires. Regardless I do think one of the existing components on the car are in need of replacement or repair but it could also be it just needs some sort of lateral location device.