I am assuming he means a liquid wrench and not lead (e.g., rust away, the spray that loosens sticky bolts). Replace it - you can get it realitvely nexpensive on ebay - you can rent a socket usually from autozone for free. Then all you need is to soak it in for a day (several applications a day_ and have a breaker bar and some muscle.

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1983 560SL Megasquirted (originally 380SL)

My former Mercedes:
1985 300SD ~190k
1990 560SEL
2000 C220 CDI
1983 380SEC 102k dual-chain conversion
2000 C280 70k (sold)
1987 300DT (W124 - sold)
1972 220D (sold)
1971 220D (sold)