[SiriusHardware]

I think it's possible that Buzby's display driver actually expects there to be a 7442 fitted rather than a 7445 - isn't that what Micky had fitted when it originally emerged from the loft?

It's not just the current output capability, isn't one totem-pole and the other open-collector outputs?

I think, Buzby, that you will still be able to obtain brand new 7-segs with the correct common (Anode? Cathode?) and the exact same pinout but surviving NOS examples of the original FND507 types could very well be dim just due to age even if you can still find them.

I built a Maplin Z80 system in the early nineties, played with it for a while, put it in the loft, got it out ten years later and the 7-segs were all very dim compared to how they had been, despite the system never having been run in the interim. I looked all over for a fault and then finally fitted a set of replacement 7-segs which brought it back up to the original brightness. I have no idea what the failure cause / mode of the original displays was. The replacement ones I fitted are now twice as old as the original ones ever were, and the display is still nice and bright.