Which crank

We don't have an exact match for your operator. The 39-315 is similar, but the 39-171 is, too. Neither are exact. The issue is your link arm. Yours is not a design commonly seen on this style operator. Part of me wonders if yours was originally custom made.

For now, look at the two products I recommended. I believe these are our best options, though I cannot guarantee that either will work.