I had the plastic bottom of the "fuel pump riser" break on me also. It was in weezer. Since its 30 year old plastic, it "should" break up and eventually work its way down to your oil drain. You might want to dump your oil once or twice just to make sure you have it all. this happens alot more often than you think. When you go to replace the riser, really look down into the hole to make sure none of the pieces are still stuck in there otherwise you wont get the new one to sit all the way in. (The plastic after overheating and slightly melting over the past hundred years causes it to stick to the block.) BTW- when you put the new one in, be sure to measure the height of the pushrod before you install the fuel pump otherwise you'll be buying a new fuel pump as well.
I'm kinda parnoid, so I removed the motor, disassembled it, split the block and rebuilt the whole thing.
But then again, I'm paranoid.