I have had a Baty DTI for a number of years with the same problem. After reading this thread I took my heart in my hands and forced the lever. After some initial resistance it moved! If it hadn’t been for all your posts I would not have dared to do it. Thank you everyone, I now have a usable DTI.
A footnote into this discussion. The level has a very fine thread into the hub and can easily be broken off if the hub is tight to shift. The hub bearing is not robust either. I always alter my angle of approach by holding the base of the lever and twisting in a circular action to ease the forces on the finer bits. I keep a finger nail on the go for such purposes, Hope that makes sense.