It's certainly a possibility. The higher the mileage and the harder driven the more likely that possibility becomes. Plenty of Z's are over 150K miles on them with no issues. It's not like the CSC or ESCL issues. I wouldn't stress over it. If you need to feel better about it, aside from tearing into the front timing cover to replace them, the best thing you can do is keep a close eye on your oil levels in case the gaskets start weeping.
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2011 370Z 6MT Sport Gun Metallic | ARC | CJM | Ecutek | FI | Fujimura | R2C | SPL | Stillen | TWM | Z1 | ZSpeed | |