I live in west Texas and everything arrives via UPS. I have found that it is better to do my own repairs when possible rather than file a freight claim. At least half of the locomotives, rolling stock and structures have arrived with some damage. I really wish that the package delivery companies wouldn't toss my Legacy locomotives out of the plane as they fly over Texas on their way to the west coast. I sometimes envy O gauge railroaders who live in the northeast: large, well-stocked stores; the opportunity to hold prospective purchases in your hand before plunking down the credit card; a network of hobbyists in close proximity. Sigh!
I had similar experience with both the Santa Fe Scout set (broken truck frames within a year of operation) and with a 4-pack of NYC 20th Century Limited passenger cars (frames broken in the box). Some of the axle journal caps fell off, exposing the round end of the axle. Three broken frames also had to be replaced (i.e., the whole truck). On the good news side, all the replaced trucks are holding up well.
I don't know about the zinc thing. The trucks looked plastic to me. But I often find that I am wrong.
I seem to recall Eric of Eric's Trains saying something to the effect that if you are going to be in the hobby you better be willing to tinker. It's not the most enjoyable part of the hobby (for me) but with patience most do-it-yourselfers can manage it.
In short, to quote the Gospel, "Be not afraid". I'd just order the parts, replace the busted ones, and go on running trains.