My gut reaction is that you should leave it alone if you plan to sell it many, many years down the road. My mechanic, surprisingly, disagrees. He thinks that any modification that improves the enjoyment of driving the car is worthwhile and may be of more value to the next buyer. I get the feeling he may eat those words when these cars become *very* scarce, but do agree the 5-speed is a good idea if you plan to keep the car for a long time. Like forever. You may want to ask a BMW restoration specialist like Carl Nelson of La Jolla Independent or CSi in Fullerton.