Get a shop mechanic that you trust (this time) and ask if they can set a differential into a manual transmission. Should be pretty common in Mexico actually considering the amount of manual transmission cars available.
The shop should have all the tools necessary.
Former owner of '99 CSVT - Silver #222/2760
356/334 wHP/TQ at 10psi on pump gas!
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'05 Volvo S40 Turbo 5 AWD with 6spd, Passion Red
'06 Mazda5 Touring, 5spd,MTX, Black