. . . brush holder plate is held on by three pathetic little brass screws (5BA - if I remember correctly) which allow the plate to flex thereby affecting the quality of contact between the brushes and the armature . . .
That's if one or more of the little swine hasn't fallen out all by itself!
Not to mention the rivets that hold the brush holders and spring posts to the insulator plate working loose, or the insulating plate cracking and breaking leaving a brush in thin air. Nor the fact that the fenestrated monkey metal brush-end bearing carrier isn't above breaking and wrecking the whole dynamo sometimes.
But as CB says so elegantly, they do have simplicity on their side, there are loads of them about, parts are available and so they're affordably repairable.
By contrast, some of the furrin stuff one sees over here is a bit trickier, despite being made in many cases to better original standards. There aren't off the shelf windings available and a lot of them are quite a fiddle to assemble / disassemble, with multiple field coils, quite often working in independent pairs switched in and out according to loads. Rather like early Brit bike alternators with three wire stators.
Hard to believe maybe, but quite a few folk use repurposed Lucas jobs , usually externally belt-driven, hooked up to DVR2s. They think we're actually
lucky to have the benefit of Lucas parts, or at least don't regard them as a blot on the landscape. Having shared their struggles, I'm inclined to agree with them!