502 mag mpi valve seats
 

After a leak down test, we found a valve that was leaking #4 on my 502 mpi in a 98 272 baja... Tore it down and sent heads to machine shop.. they did complete valve job with seals etc and a new seat, one had a crack in it... I'm lookin for words of comfort.. the guy who runs the marine repair shop, (not who did head work) keeps telling me that particular block in another boat he worked couldn't hold the new seat and it broke apart and took out cylinder... He says its a common prob on this block... Is this true or just a bad head he is referring to???? Any extra advice before reassembly???

Some 502 heads have been know to drop seats but it is not a given. And in your case you didn't drop one so the likelihood is even less. Also some of the valve/seat issues can be attributed to injection issues so if you really want to be safe, have all the injectors flow checked/cleaned for even more piece of mind.