Ron:

How reliable are the turbos?- With proper oil changes and attention to function the turbo can be very relaiable. Paul Grimshaw did a survey and based on the resluts concluded that the average life span of a turbo is 137,000 miles.

How does the AW71 compare to the rock solid M46?-Very well. Flush out fluid every 40-50 thousand miles and it could last 250,000 miles. The OD selenoid and relay will probabley need attention at about 10 years of age. Both are relatively easy and inexpensive to replace.

The check engine light is apparently "on" in this car and the owner wants to sell without a safety - is this most likely a service reminder light, as the car has apparently been very well maintained? No. The check engine light and service reminder light are different. This 90 model should have on board diagnostic capabilities if I remember correctly. Check the 700\900 FAQ for directions on how to check for stored codes and to turn the light off. It is very easy to do by yourself.

Any easy checks for a worn out turbo?-Not without taking some pieces off. If you are really intersted in purchasing the car have the car evaluated by a professional. The fee he charges is money will spent.

The engine specs for a 1990 B230FT list the compression ratio as 8.7:1 - does this mean the engine can be run effectively with little or no boost?-Yes. If you use a light foot and keep the needls out of the boost range, the car will perform adequately. Use the turbo on occasion. They really are fun.

Do I have to run premium gas in this engine? What kind of gas mileage can a conservative driver expect? No, the engine can be run on mid-grade (89) octane gas. At least this what the owner's manual for mine says. You can expect 18-20 mph in the city and up to 25 mph on the highway provided the car is driven with prudence. A heavy foot will have an adverse affect on the mileage as with any car.

Hope this helps and good luck