You should really learn how to do some serious work on your bike. So it would actually be a good idea to rebuild your LHT in order to learn how to work on it. You will need some basic repair skills (and maybe some more advanced) on a three month trek. A couple of friends of mine did a one month trek from Bucharest down to Istanbul, they ran into "huge problems" from time to time which I (with basic skills) could have fixed in five minutes with just the basic tools.

So, in other words, learn how to work on your bike. It is not rocket science.