Flex disks.

But. Here's the thing. Sourcing a decent 722.409 will be your hardest task. Because so many of them have gone faulty good second hand units that don't require near seals or K1 or K2 valves are scarce.

I have put three replacement transmissions in the 260e. In frustration at getting a good one I actually installed a 722.3 instead. (As mentioned above this was less than satisfactory.).

If your car is worth it, it maybe of more practicality to have your existing unit rebuilt.