TWIN-X 2-Speed rear end

[lee in bend]

I have one of these rear ends in my Victoria and need to know if anyone can tell me anything about how to maintain it. I try to shift it only at very low speeds as it tends to grind a bit at higher speeds and that isn't good. Been told these are not common and am considering changing to a Mitchell and preserve this unit. Talked to Steve Mitchell about it recently at the NW Regional Meet in Bend, OR. He said he'd never seen one of these. Thanks in advance. I don't come to Ford Barn often but I'll come back to see if anyone has any info.