Hello, my w124's auto tranny has started acting up very badly after a botched trans service. I accidentally removed the large allen on the drivers side of the transmission thinking it was the fill plug. well the what i presume to be "valve" fell out and broke apart, it was very tight to put back together so im guessing i did something wrong. i need some help, what is the "valve" called and is it easily replaced?

Im talking about the allen seen here under the cooler line. thanks for the help!