With this https://en.wikipedia.org/wiki/1991_Sino-Soviet_Border_Agreem... I think border disagreement already solved. Besides, I believe they realize the contention between them only strengthens NATO over them. I think the possible conflict nowadays is influence over central Asia. However, they might share the influence with China got the economic influence and Russia got political influence. It is interesting to predict this balance post-Putin though.

I mean, that's for now. Russia and the US also signed an agreement over the Ukraine in 1994 and look how that went.

That's why if one of the parties goes caput the balance might be disturbed.