If a Z3 had Cat D (now known as Cat N) damage in the last let's say 10 years it could be from as little as someone breaking wind on the bonnet. That's almost not an exaggeration.
If a car has Cat D damage in the first say 3 years of it's life then it suggests something rather more extensive and expensive.
2 important things to remember:
- Cat D is non-structural and doesn't even need to relate to an accident. It could have been keyed extensively for instance requiring a full £3-5k respray
- Cat D is a financial convenience for the insurance company. They will write a car off that needs £500 of repairs if it's cheaper for them to do it once they account for processing overheads like staff time and hire cars.
But in no situation would I ever consider a Cat D to be a scrapper based on physical concern that it could never be repaired satisfactorily. The key things is to make sure it's been repaired properly.
Even Cat C doesn't have to be a scrapper (and often isn't on newer cars). And sometimes there are thin margins between Cat C and Cat D. I have a Cat C Z3 I rebuilt myself (no alignment jigs required) which should have been a Cat D as there was no structural damage. Cat A and Cat B are the only Cats that are definitely, always scrappers.
I bought a repaired Cat D Peugeot 2008 for my daughter. It allowed me to buy a lovely car that there was no way she would have had otherwise - no way would I have put her in a car that was unsafe. It needed a new headlight, a front end respray and a new stub axle/suspension for good measure where it would have hit a kerb. It went on the 4-wheel opti-line after I bought it and all perfect. However being a newer car I wouldn't have bought it unless I could satisfy myself of the damage originally done. In this case I knew from a combination of the seller and reading the repair.
One other thing to bear in mind. A 1 year old car be absolutely crumpled all round but not written off because it's viable for the insurance company to fund a repair. That's exactly what happened to my brother's from new Z3 in a motorway shunt. It was repaired to an exceptionally high standard and no record exists of what happened on the car's history.
Back to your friend's possible purchase. A 3.0 Sport Cat D'd at 1 year old would have suffered some wide-spread/extensive (not the same as serious) damage to be written off. Does that make it a bad car - no way if it was done properly. Does it matter anymore on an 18 year old car. For Cat D I'd say probably not. In fact there is a risk of getting hung up on this when there are more important things to check out. The big factor for me would be price. Cat D doesn't reduce value as much as Cat C does. I'd expect to pay 75-80% of normal value. My bottom line - it's a brilliant way to pick up a cheap older car. Or a cheap newer car if you can satisfy yourself it was all repaired properly. But make sure you pay the right price. And make sure you never pour a ton of money into a Cat D (or even more so Cat C) as you'll never see it back again like you might a non Cat'd car.