You may have some crud caught underneath the seal. Not familiar with that specific style, but you might remove the seal, clean things up, then momentarily open the supply line to flush it out (use something to keep it from spraying all over), then reassembly. When you disturb pipe, you often dislodge crud in the lines.
Also, you might want to check your water pressure. If it is excessive (over 80psi), you should install a PRV and expansion tank. If you have one, it may have failed.