[Rovernet] Diff/drive shaft o-ring question

[FRANK SOMMERS]

Hi there, I am in the process of doing the rear brakes on my 67 2000TC. While putting things back together, I replaced the o-ring on the retainer on the passenger side. When I went to do it on the driver side, no retainer or o-ring. Either I set it somewhere and immediately forgot, it dropped off and rolled away, or it was never there. 

Has anyone experienced this before? The manual says to replace the o-ring when equipped but is having an o-ring on one side and not the other a thing? Can I put it back together without it? 

Thanks for any help

Frank
Kingston, WA USA