I have an old MTB that has three cables running under the bottom bracket, both deraillers and a chainstay mounted u-brake. It seems hopeless to keep this area clean to begin with, and lube just attracts dirt all the worse. How should I service this? On my road bike I never had issues just putting a light oil where the cables rub on the guide. But on this MTB I road 12 miles of dusty trail today and the clean and lubed area I started with looks like a cinamon glazed donut.