Mark, you probably already have visited this site.....

https://www.oldcarsweekly.com/features/putting-the-ticktock-back-in-your-old-car-clock

Maybe a bit more persistence with the turning back idea?

From another site:

Yep, but if it's been properly serviced, it can be made to keep good time.If it's a '60s era Borg clock with a second hand and no fast/slow adjustment, the trick is to wind it ahead 12 hours if it is slow, and back 12 hours if it runs fast. Keep doing this until the time gets close, then just make the small movements to keep it on time. Eventually, the clock is calibrated in this way, and "learns" to keep good time. My '68 Toro clock gained 10 minutes a day at first, and took several backwards winds to get it to slow down. Now it is just about perfect.

I even fixed the Geo. Borg clock in the '37 Olds I'm currently restoring. The first thing I hear when I throw the battery switch is the clock winding "click". Cool!!