If you are going to take the transmission apart, a few special tools might be required…Basically, you will find it’s put together with circlips and snap-rings. Plan on replacing ALL the bearings at this point…Syconizers too. A rebuild kit may be available containing all the wear parts…The bearings supporting the counter-shaft are usually loose rollers, which can be very tricky to re-assemble…The syncros can have little spring-loaded do-dads that like to fly around…The first one you do can be a challenge… Find an exploded-view parts diagram for your transmission and study it…
Sometimes a used salvage-yard transmission provides a good option…