My truck will not engage in 4WD. I can shift it into 4WD, but It makes a HORRIBLE clinking sound and doesn't want to move. I've been told its the actuator, but that is a vague term. I've called 2 places, one of which said it was part # PA33-27-790. There are none of those in the US and only 5 in Canada. $243.55 plus shipping. Before throwing down that cash, I checked Chiltons to be sure that was the right part. The Chilton's is so confusing, I can't figure out what to buy to repair it. Can you help? Thanks!