If you want to escape from GST, best to import the watch to an address in Langkawi or Labuan. Then get someone or yourself to pick it up there. Hopefully you don't get stopped at the entry point coming home.
For the last year and the half since GST was implemented, the customs operations at the packaging centres with regards to GST was still work-in-progress. They have now streamlined the operations and it would now be difficult to courier through a watch without being detected and charged for GST.
I would also recommend that you don't underpriced the value of the package. It would be better for insurance as well as for GST calculation. Customs can, if they do not believe the value on the manifest, to revalue an item based on their understanding for GST purposes.
If you do sent a watch for repairs overseas and it got stopped on the way back, bring along all the documentation to proof that the watch was yours in the first place and the purpose was just for repair.
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