you'll be fine. All the Ferrari's and BMW motorcycles has nikasil blocks and they are running strong. Also the gas is getting lower and lower in sulfur. In about 2 years from now the gas in the US will be as clean as EU gas or even cleaner ! Do not sell unless you have to, always lose on trade's !!!
that is my 2 cents. also the '91 has a lot more sensitive points by now, for example all the rubber bushings, etc. lets face it everything ages even us, so why the car wouldn't ? Even with low mileage there is some weak point of an older car. If you or the owner kept it in shape that means "chancged everyting that needed to be changed wheather it was bad or not, then it is a good car, but you'll never know !!! Unless you buy it from somebody here on the board you could ending up buying a lemon !