Help with Alembic F-1X/Clarostat Pot

I'm cleaning up a friend's preamp and need to replace a pot. It's a Clarostat, the back is stamped:
Alembic
475-001
20 9818
Mexico

I'm replacing because it tested linear from 0-380kOhms (1-8 on dial) then dropped sharply toward 0 (from 8-10). Based on that line's trajectory, I'm guessing it's a 500k pot, but if anyone could confirm that would really set me at ease for replacing. Also, by any chance does anyone have a wiring diagram so I don't have to decode resistor bands to test everything? Thanks so much!