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I've assumed these were chrome plated articles, which are meant to be bright and shiny on exterior, since pot metal is used as base metal on decorative trim items.

I'm wondering if coating the non-decorative sides of these chrome-plated die cast pieces with some impervious material which can entrap or encapsulate moisture within the piece is better or worse than leaving the piece as-is so that it can breathe naturally? I don't know the answer.

I can say that almost all of the diecast pieces on my '34, some original and some replated in the 1970s, have survived in generally very good to excellent condition, the one notable exception being the left rear tail light stanchion. All they ever had for care was an annual waxing of the plated surfaces. Of course there are many differing alloys of "white metal" and some no doubt have better survivor properties than others.

The starter switch bezel on the dashboard of my '55 Clipper broke off and an examination quickly revealed that it was pot metal. This particular piece is partially held in place under spring pressure, so if any piece needed to be made of tempered steel, it is this one.

Pot metal really represents cost-cutting at its worst. It's not long-lasting, it's subject to weak spots, and finding decent replacements is difficult. There is no way to repair broken pot metal as far as I can tell and I think trying to seal it is a waste of time.

This is an area in which 3-D printing has a good chance of remaking pot metal parts into stainless steel. I honestly have no idea where I am going to find another starter switch bezel when this one finally breaks.

Pot metal really represents cost-cutting at its worst. It's not long-lasting,

We sometimes fail to remember that cars were engineered and built to last perhaps 15-20 years at the most, not half a century and more. Packard wasn't making $1000 profit a car anymore after the 20s, and in the 50s every penny spent unnecessarily was viewed as one step closer to closing the doors.

It wasn't really for cost cutting. Die casting is essentially injection molding for metal. It offered a way to make detailed and complicated parts. The base metal had to be designed to flow well. It was plated for aesthetics and protection, but as said, 70 year life was not the target

If you REALLY want to see potmetal go bad, examine some Lionel, IVES or Dorfan toy trains made in the twenties and thirtys. I've seen potmetal castings grow two inches and more.

MrBubble
I do a fair amount of looking and searching for things I didn't know I needed. I'll keep an eye out for your starter switch bezel. If possible, post a pic to help me.

Steve

I agree with OD, to a point. Shed light, not doubt. If your car has been protected and cared for "properly", it's far more likely to not suffer the ills of age. Proper storage, and a twice yearly detailing, goes a long way for paint as well. But what is "proper"? A term that's condition based and degree of fit for use dependent. Proper has a result. Improper does too, just not desired. Best practice applies generally.

What we refer to as "Pot metal" aka, zinc die cast, is zinc alloy in various formulas, so it's not as stable as 316 stainless steel. Colloquially, these terms have many meanings, "white metal" can also refer to tin/lead bases not used in these applications. Some die cast is lead based. I'm not referring to those.
The alloy composition, it's inclusions, surface treatment, and what it's subjected to, will in large part determine the stability of the part. One has no control over these, except care and storage conditions after acquiring. It could be great or already corroded inside or out. But corrosion requires things, oxygen and electron path, to proceed, and those can be interrupted.

Note the military test requirements in the two mil specs, C-11796C and 81309E for the VCI products. Much more severe than your garage.

PS: the bezel part may also be able to be made by machining, engraving, and followed by plating. I'd suggest to take it off, take digital photos, and make an impression now, so it can be duplicated later.