Ray,
Problems selecting neutral can often be caused by the clutch not freeing comletely. This may be down to oil on the plate or a distorted plate or maybe a collapsed spring causing the plate to lift on a tilt.
Oil on the plate can be overcome by blocking the drain hole in the bellhousing, pouring about a pint of petrol in through the inspection hole, then lift the clutch and operate the kick start about 20 times to spin the plate, then drain the petrol. Make sure you regrease the release bearing before replacing the inspection plate.
A distorted plate or collapsed spring will, of course, require a strip down to remedy.
If your Mk3 Sports and Mk4 have their original gearboxes, you will find the gearchange slicker on the Sports - this model had some detail changes to the selector mechanism which improved its operation.
Regards,
Eddie.