diff --git a/models/ows_models.py b/models/ows_models.py
index 90e7c20..69fd4b1 100644
--- a/models/ows_models.py
+++ b/models/ows_models.py
@@ -163,9 +163,9 @@ class ResPartner(models.Model):
     def migrate_machine_access_from_old_fields(self):
         """
         Migriert alte vvow_* Boolean-Felder in strukturierte ows.machine.access Einträge.
+        Das Freigabe-Datum wird aus dem Änderungsverlauf (mail.message.tracking_value_ids) extrahiert.
         """
         mapping = [
-            # (altes Feld, machine.code)
             ('vvow_holz_sander', 'bandschleifer'),
             ('vvow_holz_felder_bandsaw', 'bandsaege_holz'),
             ('vvow_holz_felder_jointer', 'dickenhobel'),
@@ -193,33 +193,36 @@ class ResPartner(models.Model):
 
         MachineAccess = self.env['ows.machine.access']
         MailMessage = self.env['mail.message']
+        TrackingValue = self.env['mail.tracking.value']
 
         count_created = 0
+
         for partner in self.search([]):
             for field_name, machine_code in mapping:
-                if getattr(partner, field_name, False):
-                    machine = self.env['ows.machine'].search([('code', '=', machine_code)], limit=1)
-                    if not machine:
-                        continue
+                if not getattr(partner, field_name, False):
+                    continue
 
-                    # Suche nach dem mail.message, das die Änderung dokumentiert
-                    body_snippet = self.fields_get([field_name])[field_name]['string']
-                    message = MailMessage.search([
-                        ('model', '=', 'res.partner'),
-                        ('res_id', '=', partner.id),
-                        ('body', 'ilike', html_escape(body_snippet)),
-                        ('body', 'ilike', 'Ja')  # oder ggf. 'True'
-                    ], order='create_date ASC', limit=1)
+                machine = self.env['ows.machine'].search([('code', '=', machine_code)], limit=1)
+                if not machine:
+                    continue
 
-                    date_granted = message.create_date if message else fields.Datetime.now()
+                # Änderungsverlauf durchsuchen: Wann wurde das Feld auf True gesetzt?
+                tracking = TrackingValue.search([
+                    ('field', '=', field_name),
+                    ('new_value_boolean', '=', True),
+                    ('mail_message_id.model', '=', 'res.partner'),
+                    ('mail_message_id.res_id', '=', partner.id),
+                ], order='mail_message_id.date ASC', limit=1)
 
-                    if not MachineAccess.search([('partner_id', '=', partner.id), ('machine_id', '=', machine.id)]):
-                        MachineAccess.create({
-                            'partner_id': partner.id,
-                            'machine_id': machine.id,
-                            'date_granted': date_granted,
-                        })
-                        count_created += 1
+                date_granted = tracking.mail_message_id.date if tracking else fields.Datetime.now()
+
+                if not MachineAccess.search([('partner_id', '=', partner.id), ('machine_id', '=', machine.id)]):
+                    MachineAccess.create({
+                        'partner_id': partner.id,
+                        'machine_id': machine.id,
+                        'date_granted': date_granted,
+                    })
+                    count_created += 1
 
         _logger.info(f"[OWS Migration] ✅ Maschinenfreigaben erstellt: {count_created}")
         self.env.cr.commit()