Definitely use the torch -- you don't have to burn the sealant off, but you DO have to melt it or you will ruin the fender. It is there to keep the fender from rubbing and rusting away, so use some (3M windshield selant works fine) when you put it back on.

DO NOT try to pull it off without melting the sealant or try to pry it loose, you will bend it beyond repair. My brother and I ruined both fenders on his 75 300D (W115 chassis) trying.

You don't have to set it on fire, just get it hot. the heat gun may work, too, without the risk of setting the undercoating ablaze.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!