Right, like the guides have worn away over time and now there's lateral movement as the valves go up and down, causing them to not perform as desired.
Edit: Wanted to share this response I got from a local "classic car restoration" shop when I emailed them to ask whether they would take on a Model A valve job:
Quote:
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if it’s that old and you do a valve job it normally blows bottom out
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So... not gonna use those guys.