Shprocket

My check engine light has been coming on way to often. The dealer informed me that the timing marks were not aligned and they replaced the belt/tensioner. Light came on again last night so pulled some "stuff" off the front of motor. Timing marks line up great according to my calibrated eyeballs. Removed camshaft position sensor cover and seal around the camshaft is obviously leaking. Anybody think some oil contamination will screw up the operation of the senser? Dealer replaced this part under warranty. Seems like they would have noticed the seal is leaking?