The W-pipe side is an o-ring seal. It is held in place by one long 7mm bolt.
The black rubber thing is much more than a gasket- it is a purposely flexible joint. Rubber. It can be damaged by indiscriminate use of solvents, and once it opens up it is a huge unmetered air leak, NOT a vacuum leak as it is on the atmospheric side of the throttle. It lets are to the throttle that has not been measured by the metering plate, so the car will be WAY too lean and probably not run at idle depending on how big the hole in it is.
The black rubber seal is hard to install correctly as there are washers on both sides of the mounting ears. If you leave the washers out it will bend and probably tear.
Hard to find part at this point.