Have a quick question. I am looking to buy a January 1971 manta ray that’s had a rear disc brake added to it recently. Does the “aftermarket” add on affect the value of the bike? Is it worth less than or is it worth equal to say a January 1972 manta ray that came from the schwinn factory with an original disc brake? Or is it too hard to answer because there have been a lot of piecing together or replacing parts on these bikes over the years to know which are actually all original? Obviously being made in early 1971 tells you it’s not factory.