2001 gs650 dakar tranny problems

I am wondering how hard it is to open up the tranny on a 2001 f650 gs dakar bmw motorcycle. Mine will only shift from 1st to nuetral and no further. A friend said it was probably the shift fork that broke, but it also overheated around the time this problem started and I read a memo from BMW that said the synchros are plastic and can melt if the bike overheats. Has anyone ever dealt with this kind of problem? I am thinking about ripping into it but I also am looking for a manual...that would be helpful! Yantra