I’ve finally broken lurker cover to say you’ve done some very nice work indeed here. As you’ve no doubt discovered it’s a fine line between not enough & too much. Although maybe there’s more leeway than we think, given that in any line of rolling stock we’d see quite a wide spectrum of weathering, so it would be more unrealistic if they were all weathered the same.
I’m a broken record singing the praises of the other handy weathering medium – pastel chalks. Scrape a fine powder off sticks of various light brown shades & use a soft brush to dab it on to taste.