Man, what's up with Nissan and timing chains? The KA24E engine in my 240sx had a chain, and the guides would disintegrate on those pretty regularly too. The problem is, when they were gone there wasn't really any noise to notice (the damn fuel injectors were so loud many people mistook them for the valves, but I digress). Over time, the chain slapping against the housing would wear through - it was either the back of the water pump or the front of the block - I forget now. Anyway, the end result is coolant everywhere and a very expensive repair

Glad you got it taken care of!