Had one for 9 years 2001 model. Most common issues I came across, fractured wiring loom that goes from rear wing into the boot lid, once it goes it will mess the electrics up, had mine replaced by BMW with a new loom but can be repaired and the wires soldered back. Driveshaft clunk which can can be heard when selecting first gear and when changing up through the box so check any excessive driveshaft play. Mine did this but only very minor. Think it was down to the rubber doughnut driveshaft dampner that perishes. Noisy vanos. On early models the radiator fan housing can disintegrate with resultant damage, later models didnt suffer this. Inner sills will very likely be rusted which is hidden by the outer sill covers so get them off to check behind them. Same with fuel tank straps which rust away together with usual brake lines. The body is pretty rust resistant though. If going for a 2.8, 3.0 or M definitely check boot floor for cracks as spirited standing starts stresses the diff mount popping the boot floor welds. Check for boot water ingress through boot mounted brake light and perished wing mounted aerial grommet you normally see condensation on the underside of the bootlid. If the airbag light is lit this is usually the passenger connector under the seat that's been disturbed. The hood can leak from blocked drain seals on ends of the windscreen header and from the rear of the hood where its anchored to the body.
Apart from that a good one will be enjoyable to own but they're no sports car, I would always go for the M sport model which had better seats, lowered springs and light up gear knob
I changed the hood on mine which was originally black and swapped out the fake bonnet vents from the body coloured ones to the chrome. I did have some lovely AC Schnitzer alloys on it at one point but had issues with tram lining so swapped them out to a narrower front wheel as per the factory spec which cured it.
Would still like another either a 2.2 or 3.0 later model as I think they still look great but good low mileage examples are starting to increase in value now.
Tim.