So has the top saucer failed since?

The picture showing the J2 pin header has some cracked solder joints, worst are pins 1 and 2 which are for each flipper.

A short circuit/locked on issue with the saucer coil would have blown the 1 amp slow blow fuse under the playfield near the flipper mechs (unless someone previously over fused that playfield fuse). So provided the playfield fuse is proper spec, F4 on the rectifier board blowing is unrelated.

Out of curiosity, what are you trying to fix by doing this?

So the Saucer and Knocker aren't working. How about the Outhole kicker? If that one isn't working too then you have a solenoid select logic problem between the MPU board and the solenoid driver board.

Grab a piece of wire and strip a little from each end. Connect one end to the ground braid along the bottom of the head. *Very briefly* touch the other end on the metal tab of driver transistor Q8 on the solenoid driver board. Does the top saucer activate? If not try another transistor such as Q10 which should activate the left slingshot to get a feel for the process.
This will tell you if that top saucer coil has power and if connectivity from its driver transistor (Q8) to the coil is good.

So now you need to go upstream from transistor Q8.

Grab your jumper wire and connect one end to test point TP6 on the solenoid driver board (SDB). *Very briefly* touch the other end of the wire on the lower leg of diode CR8 which is the banded side of the diode. It should be just above transistor Q8. Does the top saucer activate?

-> If not, pull the SDB out and re-solderer any fractured/cracked joints on the Q8 transistor. If joints are good, replace Q8 with a TIP102 transistor.

-> If it does pull in, then move the jumper wire to the "GND" test point on the solenoid driver board. *Very briefly* touch the other end of the wire on pin 16 of the chip at U3. Does the top saucer activate?

The below image shows the U3 chip pinouts. Pin 16 is to the right of the notch on the short side. Note if someone previously installed a Stern solenoid driver board in your machine, Stern sometimes oriented the chips upside down. Pay attention to where the notch is to find pin 16.
CA3081_Pinouts.png

Yes, closely inspect the solder joints at transistor Q8, the J5 connector, the U3 chip and the J4 connector on the solenoid driver board.
I haven't seen driver transistors cause intermittent issues but have seen its related diode cause them on rare occasions.

Try changing diode CR8 on the solenoid driver board.

For the knocker issue, its components are driver transistor Q3, diode CR3 and U1 pin 6 for performing the similar tests.