i could definitely walk you through it. thats just a standard mechanical seal assembly. just like the ones on swimming pool pumps. i have 20yrs experience.
looks like you have most of the work done. the ceramic piece is usually wedged inside of that rubber piece. but it is not uncommon for it to get stuck like that when diss-assembling the motor. it may be stuck due to failure. as someone else said just yank on it or break it off. the motor shaft is solid steel just don't mess up the threads.
to replace the other half just remove the seal plate flip it over and find something long like a big nut driver and bash that piece out. its really jammed in there and there is also silicone holding it in.
re-assmbley is basically opposite.
make sure to carefully handle the new seal you don't want to touch the ceramic or carbon faces of either half. (wear gloves if not experienced).
the ceramic half with the rubber will need to be lubricated with some type of silicone based lubricant i usually use Aladdin Magic Lube 1oz Teflon Lubricant (it usda h1 rated basically means food safe but not sure if aquarium safe does anyone know?) just put a thin coating on the entire rubber surface don't get any on the ceramic face put impeller on table and push in new piece using clean cloth or paper towel
to install the cup and spring half with the carbon face just apply a thin bead of silicone (the aquarium stuff that home depot sells is perfect)around the edge drop it in and use a large socket or piece of pipe to bash it back in just make sure whatever you use is big enough so it fits around the edge without hitting the carbon/spring part or it will crack.
if you can make it out to my shop in bohemia i could do it for you i might even have the right size seals other wise let me know if you need help or anything pm for my number if you want to talk