Pro SD 120 back

Hello all
Just purchased the back; looks almost brand new; however, i was under the impression that the SD back had an all mechanical light seals; this one has one stretch of material along the door hinge. Where there any changes/upgrades during the production life??

Fewer light seals from the Older Pro-S model and plastic parts, but the door hinge issue always required a fabric seal. Personally I prefer the old Pro-s backs unless I am looking for a motorized back.
Pr0o-s had less plastic and they tended to last longer.