My first Pelikan (not an antique though) went through the wash and probably ruined half of my shirts. The cap came off and the nib is ruined. The body and cap seem okay. It seems that if I just buy a new nib, everything will be okay again (except my laundry). One thing that bugs me now is that the piston squeaks and jitters when I operate it. What caused this? Is now a good time to apply some silicone grease to the piston?

Yes

Use some silicone valve grease that they use in a laboratory

Believe it or not if you send the pen back to Chartpak and explain what happened they will most likely repair the pen to new condition and replace the nib free of charge.....
I destroyed the nib on one of my pens and they did it for me...
Worst case scenario, they say no... give it a try

Chances are the section/collector & feed is also gummed up with caked washing powder. I speak from experience with a Parker Rialto - and it stayed in the washing machine door seal for 4 washes before I missed it. Fortunately I was using Pelikan 4001, which is less waterproof than I had any right to hope. I never got the Rialto working properly after that.

Regards

Richard.

Wow, that's impressive! What great customer service!