$27k sounds about right, maybe very slightly high, for such a car in the used market here in the UK.

These cars are very reliable, but when things go wrong they can cost a lot to repair. Also, as the car ages, inevitably trivial things will go awry; these are no dount tolerable, but if your friend insists upon perfection, again it will cost him! Does the car have the hydro-pneumatic suspension? Apparently this can be eye-wateringly expensive if it goes kaput. Does the soft top work satisfactorily? Is the aircon OK?

The engine is bullet proof if well maintained: apparently MB has never had to replace one of these V8s under warranty.

Otherwise a $1-2k annual repair budget sounds more than adequate, especially if your friend is willing to do his own oil and filter changes.

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JJ Rodger
2013 G350 Bluetec
1999 SL 500
1993 E300 diesel T
1990 190