Rebuild is pretty cheap if you can find all the parts.
There seems to be a lack of concensus on the ability of a stuck anti-dive valve to cause a fork seal failure. At the time, I thought my blown left fork seal was related to a stuck anti-dive unit. I am not so sure now as there are respected opinions both ways on that subject. Max (in the suspension buisiness) thinks they are not related.
I can say that for my driving style, the anti-dive unit does produce a very noticable reduction in the rate of nose dive. It does not lock up the front suspension as some have said. I have progressive springs and I still bottom the front suspension under hard braking. The anti-dive valve reduces the rate at which the front suspension hits the end of travel. For me, the anti-dive seems to stretch the time it takes the front end to bottom and lessens the severity of the impact when the end of travel is reached. Under hard braking, it takes 1 or 2 seconds for the front suspension to bottom out. Without the anti-dive active, the front suspension bottoms pretty hard in a half a second or so.
Here is some rebuild info if you are going to try it yourself.
Do a search of "anti-dive" and you will find a lot of information and opinions to sort through and you can decide which comments ring true.
http://www.gl1800riders.com/forums/viewtopic.php?t=65429&highlight=rebuild+antidive