because it's the same sensor

you were unlucky to get a faulty abyssus tho

so what causes the jittering, how can it be fixed

I looked into this before and it's not really possible. The sensor is the same but the circuitry is different. The only thing you can really do is buy a new one.

I think it would be possible.
DA PCB seem to fit in the shell without even cutting anything after having a quick look at it.
Then cut of the part with the buttons and scrollwheel from the Abyssus PCB - solder some wires to it and you should be basically done. Maybe you need to solder a seperate wire for ground to each button.

alot say its pad what apd u have ?