Originally Posted by
cny-bikeman
Overdue bearing maintenance is not going to produce a clunk at a fixed point every time, but there is a likely candidate. Fixed cups sometimes loosen enough to shift under pressure, but not enough to detect when doing the typical "is the bb loose" check. It's common to feel it mainly on the right, as there's more direct pressure on the fixed cup from that side.
Although I have no wrench, yet, and the right cup will not turn by hand, a visual inspection of the area shows that the right cup is not flush against the frame, so this may very well be the issue. Off I head to the bike shop, to expand my collection of tools.
Thank you, everyone, for the suggestions.