V45 Sabre and VF700S
They all end up leaking. Possibly still available new from Honda for a small fortune. No, there is no rebuild kit.
V30 Magna (VF500C)
Ditto as above, they all end up leaking. Except, there are replacement gaskets available from Sirius Consolidated Inc. (Ontario). Listed at $7.50 CDN as of 01/04/12.
Use the Drill'n'flip method below, but replace the gasket (rubber washer) instead. I used an M3 tap and corresponding hex screws on my petcock.
For specifics, my old 'squashed' gasket measured 20.51mm to 20.63mm in diameter, 2.95 to 3.16mm thick with 5mm holes. The new replacement measures 20.1mm in diameter, 3.25mm thick with 5mm holes.
(Bo Schnick's website is apparently no more. This information is taken from the Internet Archive of his site.)
If you want a quick and easy fix for that leaky Honda fuel petcock here's what I did to one which has been working for 6 months without leaking. The simple procedure involves drilling the two rivets out, flipping the rubber 4 hole washer over, polishing the selector plate or lapping it flat, and replacing the original rivets with screws.
I took a #36 drill bit and drilled all the way through the two rivets that hold the plate on that holds the fuel selector lever plate in place in the petcock. I used a 5/32" drill bit to drill away the rivet heads that remained after the #36 drill did its work. This allowed removal of the plate, lever handle, plastic washer and spring washer.
When I looked at the 4 hole rubber washer/seal that was under the selector lever plate I noticed that it had flat spots on the raised edge around 3 of the holes whose size correlated with the width of the band on the back of the selector lever plate.
This photo should show the correlation between the outer ring on the back of the lever selector plate and the flat spots.
This seal is approximately 27 mm in diameter and the holes are approximately 8 mm.
Which leads me to think that a quick fix may be to simply flip this 4-hole washer/seal over, reassemble the selector lever plate and use the petcock. I replaced the rivets with 6-32 Allen head screws.