Absolutely gutted just been on to see a 4.2 s/c and had to walk away. Body in Andy out was near immaculate as was the engine. Was dead chuffed and ready to hand the cash over then. The old owner couldn’t drive anymore so it had st a couple of months. It was then taken on a test drive and it smelt initially like breaks after about .5 mile so got out and checked for sticky callipers but nothing and no breaks smelt. We carried on and the smell sort of changed to an electrical burning smell which we couldn’t diagnose so I sadly left it as I was paranoid it may catch fire on the long drive back. Any ideas what this could be is it common? Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

Are you sure it wasn’t due to a rear caliper sticking ? Sounds just like how i noticed a sticking caliper on mine
Did you touch each wheel to see if it was hot ? 4.2 SC - sold , now bought back
4.4 AdBlu Tractor - Stolen

Yep that was what we thought and that was the first thing we did no smells from there I’m either. It was getting worse when idling too... Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

Could have been tne alternator rectifier on the way out. Thats the smell I got a few days before it gave up. Simple fix if it was that  2007 Vogue TDV8 in Zermatt Silver with Charcoal

Good shout although that would have most certainly been roadside recovery in the way home 😂 Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

Next thing to check would be the air compressor for suspension.
I had this smell of something between plastic, breaks or coupling.
They are known to fail after about 10 years and will then overheat.