Here is the right head with the guide intact:


On the left head the top part of the guide is missing and all I found when taking the cover off are pieces I have placed on the power steering reservoir:


It could have been like this for many thousands of miles without a problem so should I worry about it now? I assume any big chunks would just drop to the bottom of the pan and any small bits that would have gotten past the oil pump screen would have been pulverized by the pump and caught by the filter. The car runs fine with strong oil pressure. What parts do I have to replace and how do I tell if the chain is worn? It has over 160K miles.