I've tried both the MY and Clarks versions of the T19 on Cartel 5513s. The Clarks makes the rehaut look too large/wide imho. If you're looking for a rep T19 Superdome, MY is the best choice. If you're looking for a flatter profile go for the gen T19 service crystal.
5513 with Clarks T19:
Same 5513 with MY T19
.... 1665 with MY T39
... and a 5513 with a gen T19 service crystal
The plastic ring ensures that the retaining ring has a pressure fit with the crystal. It's compensating for poor crystal/retaining ring tolerances (you won't find it on a gen-spec assembly). The actual bezel clips on top of the retaining ring, the metal friction washer should sit between them.
Would bend the washer you have before buying a new bezel assembly. In any case, the washer from a new bezel assembly may need bending too to get the friction right. Just Google Rolex friction washer and you'll see what they look like.