having owning both. The W210 is an evolution of the W124 chassis, Its more roomier and better appointed inside and has better insulation too - downside is the plastic coated leather compared to uncoated leather in the W124 (if you have it)

The driving feel is very different due to the steering setup of the car, It has rack and pinion compared to wormgearbox.

W210 had terrible paint, so bad that if you dont keep it waxed and sealed it will flake off like paper sheets. The evil AC evaporator is the exact same job on the W124 and the W210 - both require complete tear down of the dashboard. (If you dont DIY then its $$$ on either car)

W210 are easier to diagnose though as it can talk to a diagnostic tool, the W124 wont, you will need to get creative and oldschool with it.

The M112 V6 engine is all about midrange torque, I found it very user freindly and the fantastic 722.6 transmission is light years ahead of the hydraulic direct drive 722.3 the old cars used.

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2012 BMW X5 (Beef + Granite suspension model)

1995 E300D - The original humming machine (consumed by Flood 2017)
2000 E320 - The evolution (consumed by flood 2017)