3rd cascaded Dropdown - help

Hi, i have 2 Dropdowns, and they depend from each other(has_many). i used collection_select, observe_field to create the second dropdown, which gets populated correctly. Now i would like to have the 3rd one, which is of course as well depending from the second one. the solution i use is calling a action from the controller, where my variable gets created @..Find.. and i call then a partial. i would like to extend the partial to contain the same code as the initial page eg.: the collection_select part and the observer as well the div-area where it gets finally replaced. any ideas why this is not happening?

thx in advance