reverse

So my new to me 1987 Milano has a knocking noise in reverse gear, and only in reverse gear. While driving in reverse you hear a sound that sounds like a playing card held against the spokes of a bicycle wheel. If you lift off the gas while the car is still rolling backwards the sound becomes...

I have read in Bruce Taylor's book about the possibility of premature reverse idler shaft wear (p. 70-72). I am about to reassemble the power-train and wondering if I should replace it. Has anyone had wear issues? Has the replacement been relatively straightforward? Thanks, JP