Fellow Abarthisti, there's plenty of weeping and wailing on here and the Fiat 500 forums about how the manual gearshift can become vague/stiff/difficult to engage. Apparently franchise dealers claim that the solution is to replace the paired gearshift cables which run between the lever and the top of the gearbox. The part(s) alone cost over £200.
There is an alternative, however. The issue boils down to disintegrating rubber bushes in the cable eyelets at the gearbox end (typical Fiat problem), where they are exposed to oil, dirt and salt. The solution is to replace them with polyurethane bushes. These are available from the US from BushingFix.com - part FM1KIT2 and cost $41.94 including shipping to the UK - that's around £30! You can find the company on eBay, by searching for "Fiat 500 Abarth Manual Transmission Shift Cable Bushing Repair". Mine arrived after four days and my local mechanic was able to fit them in well under an hour. There's a good How To video on YouTube - search for JTS Builds Abarth 500 gearshift cable bushes replacement. I reckon some of you keen DIYers could do this quite easily and save yourselves £hundreds!
It's good to share...