Rebuild completed successfully.
Temps are now stable:

WD 44 C
Seagate 45 C

Case Side panel is removed, so there's a lot of air flow, but no fan.

I am now installing a temporary additional fan, waiting for the proper, silent Noctua to be delivered and put in place permanently.
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= Taym =
MK2a #040103216 * 100Gb *All/Colors* Radio * 3.0a11 * Hijack = taympeg