WD40 can lubricate my screen door so I just spray a whole can down my dipstick for every oil change.



Tranny oil is the same weight as motor oil, but because of emissions reasons oil companies are very limited in terms of what kind of additives they can put in motor oil. Tranny oils can be much more aggressive with additives because you're not going to be burning any.


Bottom line: Motor oil can do the job, but not as well. Given how infrequently you have to replace the tranny fluid, shell out the extra $5 and save your gears and synchros.