When we travel on our tandem in difficult places, like Tibet, and SE Asia, keeping the bike clean is the last thing I’m thinking about at the end of a hard day: food, a place to get horizontal and sleep are first priority, maybe changing money, buying food for the next day, trying to understand your host, the market vendors; all this before sunset since it’s often cold then, or sometimes not the best time for a gringo to be wandering the streets. So this is often when the derailleuer looks like after 3 or 4 thousand miles.
You find the darndest things when you remove a bottom bracket from the frame sometimes. This is what we brought home from Tibet and Southeast Asia. No matter how much grease you use, eventually dirt and grit find their way into your frame. We’ve brought home teaspoons of soil from Australia, Asia twice, and I’m sure we’ll bring some back from South America. If we could just stick to nice paved roads we wouldn’t have this problem, and not so much fun either.