I believe timbuktu bags are washable. The main strap wasn't removable on my bag but maybe yours is and you wouldn't have to wash the whole thing. The pad could certainly be washed on its own.

It's really no different than helmet straps or pads. In fact it's a good idea to at least rinse out the pads now and then or you may find the salt from your sweat draining into your eyes during the next downpour.