At this point, it looks like there is nothing to indicate that any of the components are 'obviously' defective.
I would suggest trying an iterative adjustment of R7.
Turn the adjuster 1/4 turn one way, and turn on the power.
If you don't see rotor rotation, turn it back a quarter turn, and reverse a quarter turn.
If still no result, try for two quarter turns, or a half a turn variation.
.... Before you start changing R7, take your DMM and measure between two of the R7 leads to get a benchmark or reference reading, so that you can have some assurance or confidence that you have returned to the original 'state' .... if necessary.... Maybe record the measurement and which particular leads they are between, before you change anything.
Components, particularly electrolytic capacitors, can change value with age, heat, humidity. .... Maybe there is some oxidation that has built up internally on the R7 potentiometer.
As additional insurance, I usually make a pair of small alignment marks on the adjuster and the component case ... a dot of paint, a marker pen, or something similar ought to work.
If Q5 isn't turning off at the correct instant, you won't achieve rotation of the rotor.