Yeah. During my yearly trek under the tank it's one of the things I do.Replaced spark plugs and noticed cracks in all 4 vacuum caps. They were cheapies from autozone. Looks like something to change annually maybe?
Some info here:
https://www.fjrforum.com/forum//index.php/topic/143379-throttle-body-caps-where-can-i-get-better-caps/