Good research SteveL.
Here in SA, I've heard of cases where Possesory Lien doesn't apply, the customer has got their car back, and the repairer has then had to take legal action to recover money owed, but I think what's written there is pretty black and white.
You need to consult the Office of Fair Trading, but until the money's paid, your mate's got very little chance of getting his car back.