It was NOS in the box when I installed it when I acquired the car in 1984.
Thirty three years of service life out of an old British NOS part is probably not something to complain much about. How old was the unit when it was installed in 1984?
I hate to disillusion anyone here, but metals such as zinc, pot metal and similar non-ferrous metals can degrade over time regardless of whether or not the product is used or even installed. For "pure" zinc castings/die castings, the culprit is well known and documented as a phenomenon known as "Zinc Pest." Look it up. In a nutshell the slightest amount of impurities in the metallurgy of the zinc can cause this. In pot metal, all bets are off. There's no fixed alloy for pot metal, and the impurities in zinc pest are rampant in pot metal.
Similar kinds of things can happen in more complex castings/forgings with other non-ferrous metals. Impurities in aluminum castings cause all kinds of problems. Some of these cylinder head castings come from what I call third world countries where the quality control isn't up to snuff, and the actual manufacturer doesn't really give a hoot. I'm reminded of a story my daughter's former soccer coach (a PHD in metallurgy for Ford Motor) told me about a container of aluminum cylinder head castings from you know where, that set off radiation detectors at the port of entry. Investigation led to the realization that the caster in this country put some spent fuel rods in the mix and thought they could get away with it.
In another story about cylinder heads, I'm reminded of the fabulous tour of the Roush Racing rebuild facility in Livonia, Michigan, where Jack Roush's team developed a process to totally rebuild cylinder heads from the legendary Rolls-Royce/Packard V12 engines that powered the P-51 Mustang along with many racing boats in later years. We were told in the tour that the average live of an engine in that plane was measured in hours. We were told seven, but records may indicate higher. When pulled off a failed engine the damage to the cylinder head was like rotted teeth and Swiss cheese. The process involved machining out the bad metal, filling it in while on an ultrasonic table, and then re-machining. The deep pocketed Jack Roush went through years of effort and mountains of paperwork to get the process certified by the FAA as airworthy. Many cylinder heads formerly used as door stops were salvaged for use in Merlin engines.
https://www.roushaviation.com. That damage to the aluminum cylinder head was due to bad metallurgy along with very hard operating characteristics.
In my life, I've run into plenty of crumbling light metal parts, that are as fragile as all get out. "Punky" my dad used to say. Many of these parts never saw any kind of fuel, they just didn't age well because the metallurgy was prone to this.
Ethanol or not, even metal is not forever.
