I bought a new MB Pro 13" in 2015, but still like to use my old 15" for some things.
I ran into the same problem with my mid-2009 Macbook Pro. Apple says it is too old to update. Sounds like a push to sell another computer.
I have been very happy with my Peak Design "Slide".
http://kphs.us/2i2gF3S Two points of contact, easy removal and heavy duty support make it perfect for my Nikon system,