If there was no noise after you lost fifth and sixth gear from inside the transmission, perhaps the shifting rod from the shifter for fifth and sixth just fell off at either end, at the transmission or the shifter.
See if you can find the source of the oil/grease. If it is impossible to find the source because of oil/grease all over everything, you should use some engine degreaser, soak it down, let it soak for ten minutes or so, then wash it off.
If and when you get the fifth and sixth gear back and no noise from the transmission, check the gear oil level, to make sure it is safe, check all the other fluid levels, then start the engine, let it idle while listening for noise, keeping an eye on the gauges, shut it off after a few minutes and then look to see if the leak is visible yet, if not take it for a short test drive and look again, then repeat a little bit longer test drive and look again and always be listening for any noise or any gauges to show warning of temperatures, etc.
Tuesday, March 13th, 2018 AT 7:59 AM