TH400 Trans Leak at Speedo Housing

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Hi all,

I recently changed the speedo housing o ring and driven gear seal to stop a leak. Well it still leaks!

After doing some research it looks as though there should have been a small spring clip holding the lip seal in position. However that was missing when I replaced the oring and seal.

Would this cause the leak? or perhaps a worn driven gear shaft is the culprit. any ideas appreciated.