Forms Data Controls :: DetailsView Accessing Textbox Through Code Behind?

I've been playing with a certain detailsview for most of last week. This particular control is located within a panel that is hidden until a user clicks a linkbutton on a gridview. Then the panel's visible property is set to true and the detailsview is populated based on the commandargument passed through the link button. What I've discovered is that with each postback, the datakey or control parameter, still not sure which or if both, is lost. I've discovered a lot about ViewState and how controls work and am a bit surprised that something as common as using a detailsview within a gridview wouldn't be handled better than it is now. I have been able to get the proper information to build a correct select statement when the user decides to edit a record. I am now working on an update statement, but for some reason while I have the right key to update the right record, I am unable to access the user-generated data that was entered in the details view.

For instance, I select record with ID of 1 in the gridview. It pulls up the detailsview and I can view it. I then click edit. The correct record is still there. (It was previously going to default). When I enter new text in a textbox and click update, the app still knows I am working with record #1 but doesn't seem to be able to find the textbox control. I have currently hard-coded a value into the field just to see if I could actually get the record to update and it did. I am using an OnInit to cause the sub to run and think this might be the problem. However, I have been unable to find a better way around this.

Here is the sub that executes on the OnInit() of the detailsview:

Protected Sub notes_binding()
If notesDetail.CurrentMode = DetailsViewMode.Edit Then
sqlNotesUpdate.UpdateCommand = "UPDATE [Oilchange_Notes] SET [notes] = '" & CType(notesDetail.FindControl("notes"), Textbox).Text & "' WHERE [vehicle_id] = " & Session("unitNumVal")
sqlNotesUpdate.UpdateCommandType = SqlDataSourceCommandType.Text
sqlNotesUpdate.Update()
End If
sqlNotesUpdate.SelectCommand = "SELECT * FROM [Oilchange_Notes] WHERE ([vehicle_id] = " & Session("unitNumVal") & ")"
End Sub

And this is the error I get: Object reference not set to an instance of an object. If I'm correct about why it's not pulling the actual value or even acknowledging the control exists and is actually 'notes' (it is), then at would point would be the best to place this code?