I also think I'm done with the part of the calibration I feel I need to do (through 5.4.8 ). From that point on (= series of XY measurements) I'm unsure a 250MHz analog scope can perform linearly enough. But flatness has been restored through the prior steps, and it's now well within specs, I feel.
As I completed this last night late, and proceeded to pour a well deserved single malt, I suddenly lost the sweep function. I don't recall if I was buttoning or whatnot, but it'd repeatedly initiate and complete the sweep sequence, without any actual sweeping (solid sine at what CW would have it). Some modules seemed very warm to the touch and the thoughts on intermittence came back to mind, but then I dove back into the SM and some late-night thinking on it - no further work, I decided - the possibility that S105 may have stopped switching started getting a solid profile, so I encircled the likely culprit on my schematic to explore in the morning.
Today I rigged some jumpers to verify my theory, and there it was - sweep was back in all its glory. Linear too, per calibration the prior day. So until I get a replacement pot (10k linear w/ DPDT or DPST) - how this switch could fail both poles at the same time eludes me - I decided to temporarily remove the "Ext. ALC in" jack and place a switch on there for toggling between CW/sweep.
Some pictures of this saga enclosed. One knowing the innards on this will see a green, a red, a black, and a white wire with some zip ties.