From what I've seen and read, the vacuum actuator is the most common problem. The part# you mentioned is what Peach Parts comes up with.
https://www.pelicanparts.com/catalog/SuperCat/3306/MBZ_3306_VENTAC_pg1.htm#item2
Several members recommend replacement of all vacuum elements at once, due to having to remove the dash to access them on a W123.