Hi, Seems like lot of people have had negative experience with the 645 and i truly feel bad for you.
I've had an 2005 645ci that i got in 2010 at 38k miles and sold it in 2017 at 110k miles. The car was purchased from a private party.
Ive had absolutely no problems with the car, the forums scared me a bit back in 2010, with all the coolant leak inside the engine, Vanos and other issues being reported. But i loved, and still adore the design, built quality & drive of the car, so I bought it without warrantee.
Throughout the ownership I stayed well clear of all the BS advice i got from the local BMW service advisors, maintained the car myself and replaced the parts and all oils as recommended by BMW on time. If it took more than 1 hour labor i would take it to my local mechanic.
Other than the branded BMW brakes i only got OEM parts for service and maintenance. Even the OEM parts weren't cheap but that's part of owning an expensive car.
I did had a very minor valve cover gasket leak but lived with it for years. Control arm bushing went away at around 100k and that all that went wrong.
Still regret selling it.
My advice:
1. Only buy one if you love the car. ( this should be true for any car)
2. find a used one with maintenance records from a car guy who bought the car out of love for the car and not merely to show off.
3. find a local mechanic you can trust.
4. Replace parts an oils at recommended time and NEVER wait for it to fail before replacing.
Good Luck
