need a new crank; the old one has come apart

also, the plastic roller on the outermost location of the outside part comes out of the thing it rolls in, so we have to go outside and put it back in; 
the window is still good, but the whole crank mechanism seems like it could be replaced
also can't figure out how to get the crank to stay in its hole; it cranks one way ok, but then it comes out of the hole when cranked the other way