I don't know if I would change the vintage instrument. I don't think so. I use my first slide all the time. I think the older trumpets had a little different tuning. The first was a little longer. If this is true on your trumpet, the saddle wont help. there are other notes that need to adjust.
Tuning is a tricky thing, I wouldn't sweat it until you can hear that certain notes are out and it bugs you enough that you have to make a change. Different trumpet or saddle on this one.