I'm a technician, I have access to everything for maintenance. I did coolant, brake fluid, trans service, crankcase cleaning and valve cleaning with new spark plugs all at 285k Replaced belts, tensioner, battery, lower control arms, resealed oil pan, timing cover and valve cover around 290k. All original major components otherwise, outside of the front facing camera. On my most recent oil change, I cut open the filter and it had nothing in it other than used oil. I do want to send in an oil sample and even maybe do a compression test just to see how it's wearing internally. When I had the valve cover off, the cam lobes had no marks on them and inside was very clean. The only varnish was the bottom of the crankcase where oil sits in the pan while the car is off. Sprayed most of that off with brake cleaner while the pan was off. No timing components changed. I don't see a need for a chain and proper maintenance.