There is no formal requirement to replace engines, but three-yearly inspections are very rigorous and repair costs are very high.
Rather than repair a car which fails an inspection on some possibly minor matter, it is prudent to sell it at auction and export it.
Documents about condition and service records are routinely forged, as are odometer"checks", but the risks involved in the latter mean that the cost of 'clocking' a car are generally confined to very high value cars. Equally, high value cars like Bentley, BMW, Mercedes are rarely driven outside gridlock, so mileage isn't an issue.
Cavaet Emptor applies at wholesale auctions, and while those who buy to on-sell often claim 'odometer-verified', they are actually just believing what a seller says. Often they get the more genuine cars if they have a reasonable trading relationship with the wholesaler.
We look closely at cars here and do forensic tests on things like dashboard screws and odo mechamisms, which show large scale interference but nothing which can be proven, especially with recent elctronic odos.
Even GM cars here can have their whole history changed with no more than a PC and [very expensive] dealer's software.
Japanese owners keep their cars for 3-6-9 years and after that it's like driving a Model T
You can find perfectly good twin-turbo 300ZX coupes from c1991 complete with very radical and expensive mods, but these cars are always snapped up by the friends 'in the trade'. It would not be a good investment to set up an engine-reconditioning shop in Tokyo.