There is a bar that connects the recliner mechanism from the knob on the outside of the seat to the mechanism on the other side, when the two are out of sync the seat back can be twisted to where one side will not latch,
to get the chrome covers off the seat needs to be removed, once it is out there is one screw at the bottom center of the carpet covered back board. then the cross over bar can be adjusted to where the recliners on both sides are in sync.
The 64 sl will have a system of cables and a tension spring that wind like a capstan around the cross over rod.
About 1965 the mechanism was changed to a rack and pinion type mechanism on each side of the seat.
Al Lieffring
66 230SL