While I don’t have any direct experience with gear oil in the TiSA Colotti 5 speed, I do have experience with other Porsche style synchro gearboxes like the regular early 1600/2002 and Porsche 356 and 911, and thus recommend either SWEPCO 201 or Redline 75/90NS with a lean towards the SWEPCO. Many, many Porsche folks swear by the SWEPCO and have for many decades. If you would like to find SWEPCO 201 locally rather than ordering it online, any shop, BMW, Porsche, Mercedes, VW… that has an SSF account, can get it for you. I would use it in both that trans and the differential, especially if it’s a limited slip. I can only guess that the diff in your car is a limited slip, at least 40% and possibly a real 75%. ?
https://www.swepcolube.com/products/swepco-201-multi-purpose-gear-lube
https://www.redlineoil.com/75w90-ns-gl-5-gear-oil
https://porsche356registry.org/archive/503