I've got some mild vortech charged 540s. Dart Pro1 heads, multiport EFI. Aprox 300 hrs on these motors and am doing top ends. After doing a leak down test I've found at least 8 exhaust valves that were leaking.
Is this just normal wear after this many hours? Or is there something else I should be watching out for?

I've got a Crane 741 cam which is apparently meant for dry exhaust. I've got long custom risers which I thought were ok for this application and I've heard there are many people running this cam with a wet exhaust. So I'm thinking this could be one scenario, although it's not every valve that's leaking on the exhaust side.

A/F ratio has always been good. I've even got a pyrometer on one of the cylinders, which showed normal temps, yet exhaust valve is now leaking.

Hours have been mostly at 3000 rpms.

Cold/static leak-down tests can be misleading. My first question would be how bad are they leaking, and are the engines down on power?
Second is, do the heads have any sort of high temp ex valve like Inconel or Ferrea Super Alloy valves? Standard stainless ex valves may not be happy after 300 hrs of blower motor.
Sometimes we can have too much info (leak down test) and create a problem that isn't there. If you're doing the top ends anyway, then it's really a moot point. Freshen up the valve job, make sure there are good quality ex valves and also make sure your springs are in good shape, or put that in the budget to just replace.
JMO

Retarded timing , or simply 300 hours the valve job is tired

what kind of exh valves are you running

4 cylinders didnt even pass compression test. 60, 80, 110 and 120. Had that head checked out and all leakage was the exhaust valves.

Another cylinder had 35% leakage and was down 10 lbs less compression compared to the other cyls.

Running Inconel valves.

Maybe, like MT says, it's just at 300 hrs things need refreshing. I was down a LITTLE on power, wasnt pulling as much RPMS. Still running 84 mph in a heavy 36' boat..

Normal wear on a 300 hr SC'd engine.