I sold my 07 ZO6 last year, so I’m not completely current. The only problem I had was the valve guide wear. The heads were replaced under my extended warranty. You can check valve guide wear w/o removing the heads. Loose valve guides can result in swallowing a valve, which pretty much trashes the very expensive motor. Lots of after-market fixes.
The stock intakes are titanium, expensive but light weight. Stock exhaust are two piece sodium cooled, can break instead of bend.
Biggest problem can be is past owners installed crappy mods and a bad PCM tune
Being the LS7 is a punched out small block there is no real cylinder walls and if those changes
are not very good can cause rods going through the block.
I would get the car connected to a full OBD-II scanner and assure the fuel trims (AFR) is correct for all engine conditions,
check to see if engine is passing the on-board OBD-II smog tests as that would give a clue how good or bad engine is running.