1998 Lincoln Town Car Oil in antifreeze

Four months ago we purchased this Town Car used from our local Lincoln dealer. It has run well and still does; however, when I took it in for an oil change the antifreeze was sudsy and appeared to have oil in it. Can this be any other problem other than the head gasket? I'm taking it to my mechanic next week; I trust him, but I'd still like a second opinion before I put $3,000 into a ten year old car. The car is in excellent condition inside and out; I'd like very much to keep it, but don't want any more surprises.