.../...a dashpot for other manufacturers and you should find one the same size (diaphragm, rod end and threaded end).../...
I have done the same, in some iterations the past decades. I can share some experiences: The various dashpot devices you can find on the market do have different "inertia" and spring force - they do not all share the same specification. But they look very similar on the outside if you put them side by side.
For your SL, you need something that has fairly soft dampening rate.
The dashpot has significant importance for the feel of shifting your gears, and for avoiding coughs in engine running when you rapidly let go of the accelerator (mounted on manual cars only).
The devices fail because the dampening diaphragm inside them ruptures