In general BSA's choice of materials was reasonably good.
A fine balance between cost & durability, weight & sturdiness, machine ability & precision

Every one who has never studied metallurgy is always over ready to criticisie & condem the use of zinc based pressure die casting alloys.
They seem to overlook that the EXAT SAME ALLOYS are in common use today for carburettor fuel injector pumps and a myriad of other critical items.

Yes there were better materials that could have been used but that goes for just about every item manufactured by man, unless it is designed to kill, maim or mutilate as many humans as possible in which case there are no rstriction on material costs so tripple vacuum melted titanium is fine.

Steel gears running in a zinc or aluminium casting have been used for oil pumps since the first mechanical gear oil pump.
The fact that after 50 years ( 80 for the early B & M series ) some are no longer servicabe is a simple fact of life, they have exceeded their planed service life, by several decades .
And the fact that after 50 years some are still running is a tribute to the original design & materials selection particularly considering the oil they pumped carried a high level of micro particles.

When it come to robustness of design, I am a testiment to just how well BSA's were made.
I cringe some time when remembering all of the horrid things I did to my first A 10 then there was the B40 I rode daily for 5 yeas with no cage left in the big end bearing. The 70 mile tip back home with on con rod on the A 10 locked solid on the crank , slowly smashing the barrels .
So I for one have great respect of the products of Small Heath .
What I do not have respect for is all the modern owners who will not ride their bikes because they klunk when you put them into gear of they leave 3 drops of oil after screaming 20 miles at 3 times the legal speed limit, ot they take 4 kicks to start or the hear a funny noise or ther is a ticking sound or,or,or,or,or,
any excust to rip the engine apart an not to ride the bike, just is case it might break done , as if that is the end of the earth .