There was a time before I was born when little men in coveralls would work through the night fixing little things that today we throw away.
A twelve year old faucet is one of these things.The new code requires all shower/tub faucets to be pressure balanced so as not to cause shower shock. This faucet is not a pressure balanced valve and should be with a baby in the house. This is just the first problem with this faucet. I say replace it with a new pressure balanced/ anti-scald type and you may sleep better at night. Oh yea, it will last another 12 years of being problem free, instead of hearing about it until you replace it anyway.
The Local Plumber
Tustin, California http://www.TheLocalPlumber.com