The crank arms are quite new, although they already hit +1600km mark. Since I reassembled the crankset (with very minimal grease on the spinde) a week ago, I've managed to ride the bike for 100km in local trails, hit curbs, climb hills, etc. The bike is well abused but I haven't had any issue yet. I do hope this will last for another 1000km. I also agree with your suggestion, I should get a better crankset in the future since I begin to hate square taper.

Interesting. did the bike originally have 700c tires and 130mm spindle length?

I'm not an expert on this, but upgrading would need a lot work.older bikes have 27" tires while newer bikes have 700c tires, they are different several milimeters. The axle length of the older bikes are also shorter because the cassettes only have 5 speeds compared to modern cassettes which have 9-10 speeds.

I have no idea what those are. but I would clean the frame and use philwood grease

...or specialized tricross (specialized.com/us/en/bikes/archive/2014/tricross) since I assume Specialized is widely available all over the world.

I agree with @Blam. Aluminum frames don't last long.

I've been in Beijing for 8 months but never saw a brand called Trac. I don't know any good bike brand from China either.