Reddish-brown bricks of this vintage have been known to be brittle and fragile. I have replaced several parts that were damaged in disassembly. Please be careful while assembling. Because most of this set is brown pieces, the pieces may have come from different production batches which may result in slight color variations that are normal and expected in sets this large. Please see the disclaimer from the Lego help pages below. Link included.
Disclaimer from Lego
https://www.lego.com/en-us/service/help/brick_facts/brick_facts/why-are-there-differences-in-parts-colors-kA009000001dblvCAA
Why are there differences in parts colors?
Sometimes you might notice slight variations in shade between bricks of the same color.
This is because we produce our bricks in batches, much like wool or textiles. All our new bricks are made from plastic granulate and to a certain degree old bricks get recycled. We do this to preserve valuable raw material and be as eco-friendly as we can with the material we use.
This is why we sometimes also recycle a small amount of bricks of a different color when we create new ones. For this reason, it’s possible that there are slight variations in color between batches.