Depends on which seal and which model vehicle, but it involves replacing the bad seal. Rear main seals usually aren't that difficult - though again, depending on the model, it may involve dropping the transmission. Front seals or crankshaft seals involve pulling the harmonic balancer (if you have one), pulling the timing cover (if you have one) pulling the old seal from around the crankshaft and tapping the new one into place.
That would depend on what oil seal you are referring to. There are many oil seals.
replace the seal
There are several types of oil leak sealant for a 1992 Honda Accord. A few of the sealants that can be used are Bar Leak's seal repair, Lucas Oil, and Blue Devil oil leak sealant.
There is only one way. Find the leak and repair whatever is causing the leak. Bad gasket, seal, or broken part, whatever.
An oil leak on a 1995 Toyota 4Runner can often be repaired by replacing the damaged gasket or seal. Tightening the oil pan bolts can also fix some leaks.
Cost of a crank seal leak repair
A 2001 Ford escape differential leak is usually caused by a bad seal. Replace the differential seal. The new seal should stop the oil leak.
It depends on where the leak is and what is causing the leak.
The cost to repair an oil leak on a 99 Ford Escort will usually cost between $250 and $500 depending on the cause. A worn seal or gasket is much cheaper than a bent pan or a ruptured block.
You probably need to drop the oil pan down, remove the front cover and replace the cover gasket and main seal.
You need to replace the oil seal.
There is a seal to seal the pan to the block. This seal goes out mostly do to lack of oil changes. Change oil then add a stop seal leak additive that closes off the leak with no harm to the engine. It works!