Is this something I need to worry about? I was installing a plenum spacer and doing a tuneup And decided to use my new endoscope and discovered the tops of my pistons look rusted and have black scaling on the then. My z was in storage for 6 years in an old airplane hanger. It started right up and drives fine. I have been driving it for the past two years with no problems. I’ll include some pictures. My Z is an 03 with 56k miles

 

Likely not an issue … run a compression test and let that guide you

 

That looks more like carbon build up vs rust. Maybe a tiny amount of flash rusting from moisture in the air/condensation if the car sat for a bit, but nothing serious. If it's really a concern for you, I recommend BG Products Aerosol Carbon Eliminator service. This service was designed with GDI vehicles in mind to clean the intake valves, but it also works for tops of pistons. You can follow up with BG 44K fuel system cleaner as well. There are plenty of other carbon removal products on the market (Seafoam, Lucas, CRC, etc). Choose whichever one you prefer. I trust BG products, I have been a fan of their stuff for many years because they actually do/achieve what they claim. If you have a higher mileage automatic transmission (Non-CVT) with a sketchy service history, I highly recommend their ATC Plus product. I've used this on two high mileage Honda ATs, both transmissions started shifting smoother (less jerk/clunk into gears), no slippage either.
Cheers!
-Icer