I don't recall any broken/cracked valve covers, just the gasket and/or the grommets get old, crack and leak.
The gasket can be a PITA because you have to use silicone.
If you don't use any or enough, it will leak.
If you use too much, it can goop out on the inside then break off and sent a blood clot down the pipe.
(blob of silicone rubber plugin up an oil passage)