High EGT

Based on your past experience it sounds like another EGT replacement is required, since it rectified the problem in the past.

You can swap EGT probes and see if the high EGT moves to the swapped cylinder.  Obviously you should do more investigating before you buy a new probe, but that would be a place to start.

Obviously 100 C is a large temperature spread between cylinders on this engine.

Mine are typically about 40 F maximum between the highest and lowest EGT's.  My #4 is  generally the highest.

I'm not clear what your meaning is about the advice from CFS?

If the throttle cable is correctly adjusted for full throttle, the ECU(s) should not be in the ECO mode and therefore the fuel flow would be high at takeoff.  The EGT's should be well within the "green" range.

Even if one of your injectors for #4 were partially obstructed or malfunctioning, 100 C higher than the other cylinders would be a lot.

Be careful with the 912iS EGT probes, they are quite fragile after they have been installed and run.  When they are delivered new they have some sort of fixing material inside the cage (at the inserted end) that holds the ceramic element safely in place.  But after use, this material burns away and the element is self supported but much more fragile.  When you remove the used probe, if you accidentally tap the probe against something, or drop it on the floor, the ceramic element will break off inside the cage.  At that point the probe is junk.