So I let it sit and watched. Seems like a small drip came out
every 5-10 minutes. I'm "thinking" (uneducated guess), that some
buildup
or something might be interfering with the seal on the valve. My
question though, is how long should I wait before changing it, or might
it be something that's just temporarily stuck near the seal and might
work itself free when the shower is used again? it just seems like 10
months is awfully quick and the other Moen faucets in the house are all
fine. Thanks in advance for any help.

I had a problem in my house with frequent faucet repairs. We get a fair
amount of rust/sediment that is not in visible a glass of water , but
certainly did wear out the faucets fast. I put in a whole house sediment
filter and instead of changing them once a year or so, they have lasted over
15 years so far.