I found it!!
The bucket ram seals were delivered yesterday, so I got started with it. This is now my sixth cylinder, so I'm getting quite good at it, but I couldn't find the dowel. A closer inspecting this morning in daylight revealed the truth - someone had (presumably) failed to find the dowel, damaged the rod-end and nut and then used a saw to split the nut (and never redrilled the dowel hole).
I've put it back together with plenty of locktite as I have no way of drilling it with adequate precision.
Unfortunately, the saw cut crosses the spot where the nuts O-ring sits.
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