Its such a shame you have an age limit, my last 2 work cars have been V8 Mercs 
If it were me, i would go and buy a 2009 530i and be done with it, the car is a nice enough drive, the engine is great, BMW warranty is joke cheap. Job done and you get full rate. I dont know how on the ball your company is, but i would then keep it looking nice and drive it until they really took issue with its age, i bet you could drive it for rather longer than officially stated.

If it were me, i would go and buy a 2009 530i and be done with it, the car is a nice enough drive, the engine is great, BMW warranty is joke cheap. Job done and you get full rate. I dont know how on the ball your company is, but i would then keep it looking nice and drive it until they really took issue with its age, i bet you could drive it for rather longer than officially stated.

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You will just about get a 2009 530i for around the ballpark, which would give you 2 years of "life" plus however far extra you can push it before they force you to change.