I could sure use some advice. 2000 Mercury 40hp 4 stroke big foot - The prop will not lock up in forward. It attempts to hold and then slips with a clicking noise. This began after hitting a stump. Since I've replaced the prop and had a local shop check it out. They replaced the (2) small springs and (1) larger spring for the forward gear ($450). But I still have the noise at low lideling rpm. At higher rpm I can't hear anything. But shouldn't the prop lock up tight in forward? It locks tight in reverse. I've checked the cables to the shifter control box and don't think thats my problem. Any help would be appreciated.