[YouTube-API] Uploading caption file using requestfactory fails, can't set language header....(.net)

Using Gdata api 2.1.0.0 and YT SDK 2.1.0.0, with WPF client uploading a caption file, I get an exception saying that the content language header is not set (as required by the api).  Using the RequestFactory to create a GDataRequest, I can set the content type and slug fine, but there's nowhere I can see to setHeaders on the Gdata request, that seems to have disappeared...  Please advise or point me in the right direction, I've tried to understand this pattern & have looked at the samples I can, no luck...

Error response string:

Execution of request failed: https://gdata.youtube.com/feeds/api/videos/WWfvx47xxxx/captions

<errors xmlns='http://schemas.google.com/g/2005'><error><domain>GData</domain><code>InvalidEntryException</code><internalReason>No Content-Language header provided.</internalReason></error></errors>


Code:

private void uploadCaptionV2()
        {
            YouTubeService service = new YouTubeService(applicationName, developerKey);

            service.Credentials = new GDataCredentials(userName, password);

            YouTubeRequestSettings settings = new YouTubeRequestSettings(applicationName, developerKey, userName, password);

            GDataCredentials credentials = service.Credentials;

            ClientLoginAuthenticator cla = new ClientLoginAuthenticator(applicationName, ServiceNames.YouTube, credentials);

            String  uploadLoc = "https://gdata.youtube.com/feeds/api/captions/" + videoId + "/captions HTTP/1.1";
            uploadLoc = "https://gdata.youtube.com/feeds/api/captions/" + videoId;
            uploadLoc = "https://gdata.youtube.com/feeds/api/videos/" + videoId + "/captions";

            Uri uriTarget = new Uri(uploadLoc);

            GDataRequest gdr = (GDataRequest) service.RequestFactory.CreateRequest(GDataRequestType.Insert, uriTarget);

            String contentType = "application/vnd.youtube.timedtext; charset=UTF-8";
            gdr.ContentType = contentType;

            gdr.Credentials = credentials;

            gdr.Slug = "Title of captions";

            String captionFilePath = "D:\\system\\temp\\Captions.txt";

            Stream str = new FileStream(captionFilePath, FileMode.Open);

            MemoryStream mem = new MemoryStream();

            CopyStream(str, mem);

            byte[] buffer = mem.GetBuffer();
            long length = mem.Length;

            Stream rqStream = gdr.GetRequestStream();

            foreach (byte b in buffer)
            {
                rqStream.WriteByte(b);
            }

            try
            {
                gdr.Execute();
            }
            catch (GDataRequestException gdrEx)
            {
                appendLog(gdrEx.Message + gdrEx.ResponseString);
            }
            catch (Exception ex)
            {

            }
        }

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