Depends on the location of the leak...Gaskets are easy, the crank seal requires dis assembly of the case and pushing the old seal or bearing out...
Some engines use a separate seal, some use a double sealed bearing...There are some sealed bearings that don't hold pressure well...The best for holding pressure are NSK with brown rubber seals as used in 3W and Zenoah engines....Found that out the hard way, a brand new black rubber seal bearing in a G26 still leaked, the engine would not run below 2600 rpm...Not enough crankcase pressure to pump the fuel at low rpm....