I wanted to share this with you in case someone is looking for replacement master cylinder brass seats.
When I had the master cylinder rebuilt, the brass seats were removed as part of the cleaning process. Not wanting to reinstall these because the seat face had flair groove scars
and I don't like reusing anything that has a compression surface because chances are it will not reseat good.
I found these brass seats on the Muscle Car Research web site (the makers of other obsolete brake components rebuild kits such as metering (hold off) valve and pressure distribution block for 1st gen.)
and they fit the GM 5460346 (WT) master cylinder on my 67 perfectly. These measure .003" (.374"-old vs. .377"-new) wider at the seat area because these haven't been compressed yet so
make sure they are centered before installing and use an old brake pipe with a double flair to push it in (for those who don't know that technique).
The price is right so stock up while they exist.
The URL is: https://www.musclecarresearch.com/gm-pd-valve-tube-seats-1
Attached is a picture of the original plugs removed from the MC with measurements. Maybe these replacements will fit other applications.
And no, I have no affiliation with MCR other than a happy customer.