Ragan 5" siezed

At least, I think that's it's name!
Anyway, when I am operating it in auto-traverse, it runs happily and then the spindle suddenly siezes. I've disconnected the drive from the side-gear
train to the quick-change gear box on the front, and the lead screw/traverse happily turns by hand. When the spindle is connected to just the idler, it runs OK. Could it have anything to do with the locking nut for the spindle-head? How do I take off the top of the housing around the spindle, to see where it's siezing? I undid the top two (8"?) Alen-Key bolts, but it wouldn't budge. Where can I get a manual for it?
Thanks for your interest.
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