The 98 we just bought has a leak (when we got it)...I crawled under it while running and it appears to be coming from the base of the oil cooler adapter/oil filter mount. Is there a gasket or o-ring there? Is this a common place for a leak?

It is a pretty solid drip when running but not at all if the engine is not running. You seem to indicate your thoughts are it is at or near the filter which is right above this area so you might want to double check for this.