Howto export private calendars on old zimbra installation

[NightTwix]

Hi,

we had a quite old Zimbra installation (Release 3.1.2_GA_445.SuSEES9_20060530181808) and did a successful update to
Release 5.0.7_GA_2444.DEBIAN4.0 DEBIAN4.0 FOSS edition.

The update was done by exporting all calendars to ics by saving this url:
http://ZIMBRASERVER/service/home/USERNAME/calendar.ics
and importing it into the new calendar

So far, so good. But there are some users who had private calendars as well and i dont see a way to export them.
On the new system i could simple export them like this:
http://ZIMBRASERVER/home/USERNAME/PRIVCALNAME

But this isnt possible on the old system. I tried various URLs but without any success.

Is there a way?