4th gear has had no real affect on driving the car other than that gear is missing. Ive drove it for almost 6months that way cuz to fix it is an expensive undertaking. It is still pretty qucik due to the fact I raced at the track and barely got into 3rd and ran a 13.60. Didnt have to use 4th. Granted it does bringt the value down and is a headache, it does not make this inoperable.
You should hope the 'buyer' doesn't read this statement before purchase! Track raced, drag raced and driven for six months in that condition. Let us know how this turns out. *speechless*