Corrosion is number one thing look out for on these, surface rust is going be the norm and that can be surface treated, heavy corrosion can get quite expensive and if it not localised rust you be chasing you tail for no long term benefit .
Also don't think newer means better, late 90's to 2002 era about some of best made .
Do good checks using MOT history and good visual inspection and that means a real good long look and poke around underneath, rust doesn't always show itself but steel can be rotted and collapse under physical inspection .
Is fairly easy find these pretty clean and not many keen on larger engines so prices can be low/easy haggle .
I would be more sceptical of dealer sales than private and that comes from 30 years trade experience lol, 99% of the good stuff comes private sales, biggest ballache and pork pies always dealers .