Imichael, hopefully the seller discovers something simple like a fuse and is able to sell it easily.
Update on my GR:
The 54" mower gearbox was covered in residue, I cleaned it all off, checked the fluid level, fluid was running out and I capped it back off.... used it for about 30 minutes and noticed the gear case was wet with oil. I then removed the plug and let it run out, there was about 12 oz too much, so that should explain the excessive venting. I went ahead and drained it and refilled it so I know it's good.
The transmission was covered in oil that appears to have not been cleaned off in a long long time. I cleaned it so I can see where the leak is... it is definitely venting fluid out of the breather but I believe there may be another leak as well. Will update when I solve that mystery.
Before and after pics attached.