If you are going to be doing any amount of freeway driving, the stock 4-speed is not sufficient at today’s freeway speeds. The high engine speed will leave you buzzing and fatigued after a long drive. Your choices are to locate a 4-speed unit with an overdrive, have your transmission retro-fitted with an overdrive, or fit a 5-speed gearbox, such as the Hi-Gear Engineering kit from Moss. If the majority of your driving will be within the city, with only short stints at freeway speeds, a 4-speed will still suffice.
Replace the seals and fill it with synthetic lubricant, such as Redline MTL.