Them tin valve covers always leaked on the Ambulance motors we built.
Even if we peen all the bolt holes used rubber or cork or what ever, they would go a few weeks or so and start leaking.
We started to put the Aluminum valve covers on all the Ford big block motors we built and no more problems.
I guess because they have a wider lip on them. A short time later they started putting Diesel motors in them,
Which was good because it slow'd the lead foot Ambulance drivers down in Michigan that kept blowing up $20, 000
motors. Our head Mechanic actually went to see how they where blowing up these motors. They would get a call in a small town
250 from no where and be pushing those big flat Para Medic units at 120 or 130 MPH the whole way pushing that wind, oh ya both ways.
That didn't happen after they went to Diesel because they were governed at about 80 mph. I left there about the time the Diesel started to come in.
Had I known what I know now, I would have stayed and let them put me thru Diesel school. LOL!!!