Stratasys Objet500 User Manual page 187

Objet500 User Guide
14. Make sure that along with the head, you remove the two rubber O-ring
Important
If the seals are not removed with the head, they are probably stuck to the
print block housing. If so, remove them.
DOC-07027 Rev. E
seals.
Figure 6-76 O-ring seals on the print head
Figure 6-77 Making sure the O-rings are not stuck to the print block
6 Operating and Maintaining the Objet500 3D Printer
6-56