All of a sudden the steering on my 2000 Grand Marquis (90K miles) has become feels harder. It used to be basically effortless to turn the wheel and now harder. Car had new serp belt at 77K miles. Took to my mechanic who said he would check it out but suggested adding some Lucas power steering treatment to see whether that would help. I added the Lucas and didn't notice any improvements. Anyone have any idea what's going on? Thanx