My Sonata has been using about 1 qt of oil every 1200 miles. Upon changing the spark plugs at 105K, I noticed three of the four plugs were wet with oil (#1,2,4), only #3 was dry. The car had sat overnight before the spark plug change. I would think this could only be caused by oil leaking from the valve stems back into the cylinder head overnight (bad seals?) The oil has been changed religiously every 5K with full synthetic oil and only Hyundai oil filters. Could this be caused by carbon build up on the valve stems making the seals fail? Would the failed seals be a warranty item?