While the weathering technique is very well done, I do get the feeling it' over-done by a ton. That much rust you'd expect to see from Nurgle, or from discarded wargear left to rot somewhere but from pre-heresy marines? Even when roughed up after a very long campaign, rust wouldn't really be that prevalent in èvery nook & cranny. Chipped paint, dents, soot, discolourations for sure but rust really represents a neglegt in even the most basic maintenance and use. In short, it doesn't look very realistic or plausible. Any military person leaving his gear that neglected would surely get chastised.
Just my two cents, because otherwise you've done a kickass job.