Cannot install/configure gstreamer with MP 1.3.68

I am unable to get the video streaming configured with MP 1.3.68 running on Win 10.
When I hit the gstream button in the extended menu (CTRL-F) MP starts downloading something and then runs into an unexpected error with the following details:

I then installed gstreamer 1.9.2 as advised in another posting, which did not change anything.
Streaming with QGroundControl works flawlessly on my PC. Also when I start gstreamer form the CMD line with
gst-launch-1.0 udpsrc port=5600 ! application/x-rtp,encoding-name=H264,payload=96 ! rtph264depay ! avdec_h264 ! videoconvert ! autovideosink
everything works just fine. So it seems that something in MP is broken. Any ideas anyone? @Michael_Oborne

One more evidence. MP is trying to download gstreamer 1.12.4 x86_64 from the ardupilot firmware site despite of that gstreamer (64 bit version) is already installed and fully configured on my laptop. Regardless, the download crashes with an “unexpected error” after about 40%-45% progress on the download. I tried to reinstall MP what did not fix it.

there has been some server changes recently, could you try again today, and see if this is resolved?

I installed the latest MP beta and gstreamer 1.12.4 64bit manually. With that, streaming now works, but I still get an error when I try to click on the gstream button in the F7 menu.