2 things spring to mind:
1. Its a 1991 Volvo ... let it be any other make, you're bound to have problems that comes with age. Rolls Royces and MB make no exception. Electronics, i.e. relay, fuses, etc are not predictable objects, but at least the mechanical components are fine as they ought to be.
2. Its a 740 - the engine was based on the 240 platform with little (if at all) any mods, which has had about 20 good years of use in them before being transplanted onto a new chasis.
I believe this 740 was one of the shortest model span for Volvo that was the catalyst in the re-thinking and design of future not-so-boxy cars. I quite like the way Volvo has designed their cars since the inception of the 740, leading up to the 940, 850 and S70. Remarkable.
But I'd still keep on to the MB.
126 tailed by a 203, 129 leading the pack.