Here is a copy/pasted (with personal info removed), word-for-word email exchange between myself and a Pilot USA customer service rep the other day:
After cleaning my Custom 823 some time ago I seem to have misplaced the small clear rubber gasket which seats around the feed as it sits inside the section (this is not one of the black rubber o-rings which sit on the outside of the section or the plunger assembly to form a seal upon contact with the barrel).
Thank you for your email message. We appreciate the opportunity to address your inquiry.
We would be pleased to send you the needed ring. What is your last name and mailing information?
Thank you for writing to us. We value your loyalty and investment in our products.
No charge. This will be sent via US Postal Mail.
Have a wonderful day!
Some things to note:
-I live in Canada; I reached out to Pilot USA because up here we don't have a Pilot office, just a distributor (although I think Pilot USA does handle all repairs etcetera for North America)
-These forums have stated on numerous occasions how picky Pilot are if you did something to their Custom 823; there are stories all over here to the tune of I opened it to clean it when the papers clearly said not to and Pilot charged a whack of money to do anything to my pen
To be fair, nothing is broken on my 823, I just stupidly misplaced a part (which so far has not impacted its performance strangely), and the part likely costs them more to post through the mail than to manufacture. But I don't see service like this much nowadays... I can't imagine opening my Nikon to clean it or adjust something, misplacing some piece in the process, and simply emailing Nikon and having them send me a replacement gear or o-ring or whatnot... and FREE to boot.
Long story short, Pilot earned a ton of respect from me for their customer service... it's nice to see a company that supports their products so solidly. I fell in love with the Custom 823 I got a while back from them, but this experience cements that I will definitely purchase from them again
(the other moral of the story is if in doubt, ask... you never know what reply you will receive!)