I'm finally getting around to doing a transmission fluid change on my 2001 Boxster S.
I've been looking through all these different forums about what the best "gear oil" is for my 6 speed manual transmission.
I gave up.
I went to the dealer and was ready to pay the $30 per liter that I've seen mentioned, but they sold me "Mobilube HD Plus 80W-90 Gear Oil" for $8 a liter. I was surprised. I asked about synthetic, and/or Porsche branded oil, but they assured me that this was what Porsche recommends for this model.
-for what it's worth...
https://mobiloil.com/en/gear-lubricants/mobilube-hd-plus