Happens too often Jase I'm afraid.
The geometry of the opening point pivot (the 'ole in the fibre bit) might be a fraction off, or the blade not made quite right slot-wise, or even the backplate, if a pattern one, might have the pivot post a few thou out of position. It's all it takes.
I believe Grove Classics, the Velo people, are now making the bits for the steel units having acquired the tooling and the rights, but haven't seen anything specific on their web site so far. If true, then we might expect some tighter QC - maybe!
If in your travels you come across a decent brass type, of the earlier generation, I'd grab it.
They are in many people's view 'better' for four reasons:
first, the opening point and spring are the LT earth side so a kiss doesn't kill the spark;
secondly, the double spring blade of the brass types is gentler in operation than the steel equivalent;
thirdly the points gap stays in adjustment longer (as a rule) for not relying on friction on sliding bits.
Fourthly, quite often, the contacts mate a lot more squarely too.
And a fifth plus point is that you get the option of an auxiliary earth brush on the back face, which can help reduce the dimpling at the firing points of the mag that is caused on the armature drive end brass piece by return current through the main earth brush.
If only someone could be encouraged to make new brass types (and the points too), it would save a load of trouble. 2nd-hand ones are OK if you get a good one where the pivot post isn't worn right down (and the points don't wobble) - but it's a fiddle to repair them.
It's also worth knowing that if you come across a decent BTH anti-clockwise backplate off, say, a KC2, that'll work very nicely too. Main dimensions are the same, the integral keyway that sets the internal timing is in the same place and the design is better too. New complete BTH assemblies can be had - but you need a mortgage. A Bosch set will also serve and is well made - but the keyway will probably need suppressing and reforming in the right place, or the camring repositioning.
