Nothing, touch wood, it's very low mileage for the age and regular oil changes shall keep that beautiful Honda motor tappet rattle free and sweet for anything up to 400,000 miles (common occurance with owners present on the Rover 800 mailing list).
Having owned an 820Si and 820e I would say I know these cars very well. People will criticise the handling but driven correctly the Vitesse handles remarkably well and can keep up with much smaller items on the B road.
Performance from the manual box and 2.7 V6 is sensational, real tarmac ripping stuff, it can easily embarass RS Turbos, BMW 535's etc off the lights.
Build quality steadily improved on the Mk1's until their demise in 1991, 1990 was a very good year, 1989 was the start of good quality, early ones were not very well built but still make good cars if looked after.
As an update to this review I did on my Vitesse, I now have a Sterling, doesn't handle quite as well as the old Vitesse, but has lots more toys, and having owned the 820Si and 820e, which were both saloons, I decided I prefer the saloon shape, also I have an 820 Turbo and 825 Sterling, Jaguar XJ40 3.6 and a BMW 528i (free).