I apparently misunderstood your reference to tab leaders and assumed that a table of contents was involved. :-(

Thanks for the clarification.

You can't change the typ of tab inserted by a list level, so setting "Follow number with" to "Space" would probably be a good start (see a reply by Guessed/Andrew).

After having defined a tab leader, you'd have to manually insert a tab character in the heading.

__________________
Stefan Blom
Microsoft Word MVP

Microsoft 365 apps for business
Windows 11 Professional