I spent ages trying to sort the same problem on mine too. For what its worth here is what i've done so far... Oil changed, not for Porsche but Millers (
Engine Oil, Gear Oil, Fuel Additive, Millers Oils). I cannot remember which one, but call them and they'll advise. Changed the shifter for the short shifter and replaced the front engine mount. The shifter was one of the eBay copies. And then spent a few weeks playing with the cable adjustments. Also the connections at the gearbox end were checked and oiled.
Now it's by no means perfect, but much, much better. One of my cables is a bit stretched so that's going to effect things a bit. As the weather is improving, so is the change. A point my indy made a while ago.
A lot of the stuff you'll read on the forums about the second gear change is actually about the 6 speed, serious problems with the 5 speed look to be less common.