Good maintenance, just as you would never rebuild your motor without replacing the crank thrust washers, you should also care about the camshaft thrust plate. Sometimes called the "triangle plate" this small but important plate doesn't just hold the cam to the block, but has to locate it within the proper tolerance. There is a bearing surface on the plate, and when that wears the cam can literally walk back and forth. The point here is that any time you have the cam plate off you should replace it, as you would with any engine bearing.