Worst case scenario? You blow up your Berg 5 speed.
Then you have to go to the wrecking yard and buy a used stock four speed. Install it, and take it easy on the drive home.
Yes, you may have to retro fit a few mounting parts, but I bet it will be easier than getting the five speed fixed in Mexico.
Not all of us are as brave as Bruce; my hat is off to him, as it made for a great story.
Four speed or five, a transaxle replacement is one job I would not want to be forced to endeavor upon in order to make a huge drive home. Used engines have a few more visible indicators as to their age/mileage/worth, but transaxles? Not so much, as far as I'm to understand.