Re-covering your CB400 seat can work out fine, as long as you get the correct grain and colour shade in the vinyl. The correct studs, the right shade and style of lettering for the rear of the seat, and of course the seat pan has had the rust removed, the damaged areas made good, and then painted or powder coated. Of course if you find this a little daunting, you could just order a brand new Honda seat, fit it, stand back and admire, then go for a ride!