MTD KH-25-313-03-S  Grommet, Rubber

The most common purpose of a Grommet is to enable a sealed connection between two components, like holding fuel lines or the fuel valve usually within the fuel tank. Usually made of hard but pliable rubber, exposure to chemicals in the fuel and abrasion from debris in the fuel system can degrade the grommet over time and eventually cause it to leak or fail. Replacing a leaking grommet is usually pretty easy using a flat head screwdriver, but rubbing some oil around the outer rim may help with installation.