Solid flat tappet cam

Well, they shouldn't move. After a few years of service and that will depend on type of service, abusive or not, the wearing does create a little extra space. You don't need alot, but it'll letcha know when it is time.

Slant 6's run with that famous "Clatter" and for a good long time as well. The mechanical cam /6's ran a very long time beofre they clattered.

If it was an adjustment every 5 years, I'd call it an early adjustment or heavy abuse. Long periods of idle/stop and go traffic or racing.