Hi Declan,
I recently repaired the traveller on my 460GL. The car had shattered during an unintentional gybe on a windy day. Like you, I found that the head on the screws on the “end pieces” of the traveller track itself were not great quality – they were slightly oversized for the alan key and so trying to remove them just with an alan key was unsuccessful. In the end a mole grip and a lot of time and patience worked. Therefore I replaced the car, but not the whole traveller (which was a relief as I expect you’ll face a similar problem with the screws holding down the track itself). I went for a replacement Lewmar car. If I was in your shoes I would either just replace the car (best option) or replace the whole track and traveller with a non-Lewmar version. Good luck. Tom