99 A4 with a 1.8t and standard transmission

I've got a new rear main seal, the thing looks like it's got an o-ring to seal it up. Also the gasket doesn't pop up on many websites like ecs or genuineaudiparts. I've searched AF and audizine and heard conflicting things, like some people say "remember to get the gasket" and some other folks say "it's o-ringed, you don't need the gasket"

so what's the deal? should I go find one (any recommendations?) or does anyone have the part number for this if it is necessary?