Brian's right, the coupler is a stinker. If you have to buy a new coupler though, they are now pretty readily available. Pelican Parts has a new couple for $115. Not bad. But much cheaper to put these new bits in. Even if you have to take it to a machine shop or something you would still be money ahead.
But while we're talking about bushings... Underneath your shifter (I assume you have a 911 type shifter) there is a cup with a plastic bushing inside of it. The bottom of the shift lever is a ball that wears on the plastic cup. Shifting gets real bad real fast if this is even slightly worn. Cheap to replace. The bushing snaps to the bottom of the shift lever and the assembly slides easily back into the cup.
Somewhere between the shifter and the coupler you "should" have another set of bushings in a little bracket. The long part of the shift rod goes thru this. I say "should" because this is always present in a 911 or a 914, but who knows on a speedster?? These are also cheap to replace, but I've seen them last for decades. The one under the shifter usually goes away first.
Three spots with bushings, under the shift lever, on the rod between the shifter and the coupler and the coupler itself.
Row row, row your gearbox...
angela