I saw a picture in "Armor Of The Pacific War" showing T-34/85 tanks moving through supposedly impassable mountains into Manchuria. The tanks looked new, if crewed by veterans. I'm using the Academy T-34/85 and wondered how I should age and weather it.

This might be worth a watch: https://www.youtube.com/watch?v=HjygZML_X-o

The Manchurian operation was 2 pronged attack with forces moving through mongolia and a mountain range between vladivostok and manchuria. Moving through dry plains and later bogs and marshes. One thing to note, the beginning of combat operations coincided with the start of the monsoon season in the area.

A bit of weathering would be in order, I'd say.

Dimitry Loza's book might be a good read for you, even though the tanks are Shermans, a lot of it deals with the logistics and such of the Manchurian campaign.
http://www.amazon.com/Commanding-Red-Armys-Sherman-Tanks/dp/0803229208

Just bear in mind that the Academy Factory 112 kit represents a brand new 1945 production model, and the Manchurian campaign lasted only a few days before Japan capitulated. Paint fading would not be an issue. Just some dirt on the lower parts of the vehicle would probably suffice, using washes or airbrushed filters, followed up with a little dry pigment or pastels. If you want to depict wetter terrain, a muddy suspension can be depicted using epoxy putty, or Celluclay or even tube acrylic paint with some grit added. Pin washes will bring out fine details.
And I agree, Dimitri Loza's book is a good read.