Cat 980c with tappet/pushrod noise ?

HI everyone ,was looking at buying a Cat 980c,but it has a top end rattle ,maybe the head or just a pushrod .
It apparently still runs ok and doesnt miss a beat ,no engine miss ,the rattle has just happened recently and they say that the Cats were prone to having pushrod problems.?
Can anyone elaborate a little if they know of any issues with the top ends..not sure if it is worth getting into..I need it for a bit of clearing here and there ..