So, just when you think you've heard it all, I just stumbled upon some info I've never heard of before. In Europe, SOME of the late model, or post-facelift S13's had defective intake valves from the factory. There was a manufacturing issue and there was a batch of intake valves that weren't properly heat treated, leaving them weak. They would deform to the point of being razor sharp at the edges and stop sealing properly and this would happen at low mileage. The defective valves are stamped with the number 74. But not ALL 74's are bad. It was common to have a head with good and bad 74's in them. Nissan even issued a TSB on them and they were replaced at no charge if the car was still under warranty. This should not be an issue on any 8 port head. Nissan ended up changing the part number for them and the newer intake valves are stamped with the number 51.
Of course when I read this I freaked out and started going through my rebuild pics to see which intake valves I had. Fortunately, they're all 51's. Apparently my head was one that had the issue, and then had the valves replaced.