I raised the OEM issue with the repairers and was told that it's a bit of a misnomer as they're all made in China and probably from the same source.
The machine seems to be working perfectly well and is as sensitive in terms of pen drawing as it was previously, how long it lasts is anyone's guess.
Before buying my SB3 I'd contemplated getting an Asus Zenbook Duo and now I wish I had.