My first Cossie was Cat D accident registered in 1996 (I bought it in 2004). I got it a bit cheaper cos of it, and in the end it rusted to death and is being reshelled at present. The fact it was listed never ended up mattering at all in any way, it just saved me money.

Personally, the fact it's 18 years ago means that any problems would have arisen long since, so I'd go for it. If it was stolen/rec 1 or 2 years ago, I'd stop and think about it, and want more money off probably.