Welcome to the Forum!

As you already know how to access the o-ring, I'll tell you how to clean and lube it. (I can't tell you how to get to it from memory )

Fill a bucket with water and gently roll the immersed o-ring between your fingers, all the way around. Then use a Teflon or silicon based lube (petroleum based lube wrecks o-rings!!!) and, again gently, massage it onto the o-ring. (By 'gently' I mean DO NOT pull on or stretch the o-ring as you do these things)