Just so I know, what is old to you? I bought my first Holley blue pump in 1984. The second a year later (for my tunnel ram set up).
By 1986 I had to have both of them rebuilt. The company that did them said they had garbage brushes and they were made as cheap as they could be.
After he went through them they were more reliable, but the biggest thing that made them reliable was the return line.
LOL…I’m down to one 250 pump and I’m using that one. They aren’t coming up used so much any more. Pretty good swap meet coming up in January and another HUGE one in April and maybe I’ll get lucky and find a few.