[Walt Fricke]

I don't find these plugs separately listed in the factory parts catalog. Not in the diagram, anyway. I believe shops just make them as needed. It is an interference fit, so some skill in measuring and working a lathe would be in order.

I think the factory 993 shop manual (google and download) gives some specs on these, and part numbers, though whether they are the same size as your early 930 case I don't know.

Another benefit of having a set of pipe thread taps. You can buy those plugs in any good hardware store.

Walt Fricke