High quality OEM Spec shift shaft seal.
The axles seals and shift shaft seals can be installed with the transmission in the car. The input shaft seal can only be installed with the transmission removed. There is no “seal” for the case halves; they use a special anerobic sealant (not RTV). If you need to reseal the case halves, I can talk you through it or do it for you. Don’t use brake cleaner or paint on the transmission once it’s assembled, as it will dissolve the anerobic sealant.