[71tahoe]

You didn't say which engine but every full gasket kit I get for a SB v8 has 2 different thickness rubber gaskets to go between the pan and the block front and back. I test fit to see which thickness to use and then run a bead of sealant. Someone may have used the thin one and filled the rest with sealant or the old seal may be deteriorating. Oil pan seals shouldn't be very expensive. (Intake seals are about $8 EDIT-- actuall closer to $10. found some for $12 at advance auto aka partsamerica.com) You can usually drop the oil pan without removing the motor depending on your setup. I remember doing a re-ring on a friend's 400 SB with it still in the truck.