Install a new spur and slipper pad and a new locknut that puts the tension on the spring for the slipper. Tighten it all the way until the spring is fully compressed. Don't over do it or you'll warp the spur and it will burn up anyways. Next you need to set your gear mesh tighter or your clutch is overheating the clutchbell causing it to melt the spur. No a metal spur is not the answer.
Clean the CB good, grease flings out of your new clutch bell bearings and goes all over the clutch shoes and clutch bell. This causes slipping/heat..... you get the picture.
I recommend an aluminum clutch with a .9 spring, this combo will run nice and cool, preventing the melting issue.
Big power engines are not as forgiving on gearmesh. As long as I was close to a good mesh, my NS-25 would not strip the spurs. Once I stepped up yo a stronger engine I figured out I had to set the mesh as tight as possible but still be able to spin the spur easily for at least 3/4's a rotation. One little tight spot in the mesh is no big deal with a plastic spur. It will wear in and be perfect. Follow this advice and your spurs will last longer than your dogbones. Which you better stock up on, the Picco will snap them like twigs.
After you solve these issues and get a good tune, your shifting will be more consistent.
I recommend 17/47 gearing and you'll need to tighten the two speed shift point a good 1/2 turn or so depending on what you where running beforehand.