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Hi Dave!
This sounds like an attempt, as you suggest, to eliminate overpressurization. Did you see my references to Caquot's resolution of the similar problem on the 220 H-S's? With 10,000(!) 220's being considered unacceptable for service, he was called in to find the problem. He tested a group of engines; "salade" is the interesting term used to describe the appearance of the failed internal components. He installed a relief valve to eliminate the fracturing of the transfer tube which fed oil to the reduction assembly. This thin-walled tube tube burst- when the engine operated in cold regimes- as the pump kept pushing the "tar" into the tube. I doubt if any of the modified engines arrived at U.S. units prior to the war's end. Thus Hartney's "Damn those SPADS!"
The same consideration plagued the P-38 in England: the oil coolers froze up creating "The Allison Time Bomb" and as a consequence they were transferred out of that Theatre and shipped to warmer climes in No. Africa and Italy. They re-appeared in England later- possibly with mods or perhaps they were limited to the Summer months? The P-40s and P-39s operated in ie.Russia, without notable problems so perhaps it was a Lockheed design flaw in the associated subsystems rather than a engine problem per se.
It appears as if the later designers- at least at Lockheed- didn't learn from the problems of WWI engine operations at significantly reduced temperature. Perhaps the information was something the French considered not to be disseminated?
Did you get your metric tubing? "Maryland Metric" in Baltimore supposedly has it in inventory.
Happy New Year! Lee
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