If you lost most of your diff. fluid you did yourself a big favor by not driving it any further. Sounds like your CV joint died and the heat may have taken out your seal on the diff. Even if that's not the case and only the cv joint is about gone, you don't want it to seize up at speed. Maybe you've had made it but at what risk. At worst the $500 was an insurance policy and in my book money well spent.

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LRG
1987 300D Turbo 175K
2006 Toyota Prius, efficent but no soul
1985 300 TDT(130K miles of trouble free motoring)now sold