What I would do is remove from the mower separate the two covers clean it out and replace the oil and give it a try.
Or look on the top for a black cap and just add some oil.
Worst thing that can happen is you get to see what the inside looks like.
Look on Craigslist and find a $100 mower and use the tranny off it.
Or find a small shop and see if they have one laying around.
(( racing is the only sport that you need two balls ))