Trigger houding oil holes?

[CrossedCannons]

Question appeared on another forum and got curious too to fill another gap in my Knowledge, but when was the oil hole, typically found in the Inland/Winchester T5 trigger housings (RHS) (Riesch), drilled on non Inland/Winchester trigger housings?

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[painter777]

Many would have been drilled during late WWII re-builds, after the adoption of the lube/drain hole was introduced on the Type 5 housings.
I'd guess the majority of the other Trigger Housings had the oil lube/drain hole added during the Post WWII re-build programs by Underwood, Stan Pro and the Arsenals.
Lucky that many never had this done.
Someone may know a more precise date. Or dated document as to when this was implemented.
BrianQ comes to mind for these matters.

Regards,
Charlie-painter777

[jimb16]

Many were done when the carbines were upgraded for Korea.

[CrossedCannons]

Good to know, thank you. I've often weondered where they came from on earlier housings.

[Bruce McAskill]

About August 1944 for the type 5 trigger house with the oil hole.