As a diesel it will probably not be too bad, it was the petrol versions that suffered with the Head Gasket failures. That said its a Rover, well an MG badged Rover and its never going to be the greatest, smoothest car. The build quality was never the best but it depends what you want. The only other possible problem is obscure spare parts are very difficult to come by should you need anything out of the ordinary, I am led to believe that things like intercooler hoses and clutch arms were very scarce at one time, they may still be? If the price is right though it may be quite a decent buy.

K-Series head gasket issues aside the 1998-2004ish Rovers were actually pretty good quality, the car you're looking at had quite an old (Rover L-Series) design diesel, not particularly refined but being an old-school design it can wrack up interstellar mileages. No DMFs or particulate filters to worry about, excellect fuel economy and they'll run on just about anything - lots of DIY biofuel brewers running these engines. They are brilliant handlers - the chassis was very well sorted without being too harsh.