I noticed this problem through the winter. For about six weeks, I didn't drive much. It would set for about 10-12 days, then, I would start it up and take it for a drive. Noticed a small amount of smoke and oil smell. Opened hood and noticed oil, on left side of block. Cleaned it up, tightened cover just a bit and it's been fine. I think what happens is that it gets down to 10 degrees, metal shrinks, you start it up and it expands, thus, leak. Since it's warmed up and I tweaked the covers a bit, no more leak.