Small Engines (Lawn Mowers, etc.): crank shaft seal, crank shaft, shaft seal

Question
I have about a 93 Simplicity 18hp Vangaurd. Mice filled the engine housing full of grass and young ones. Engine got pretty hot and yes ruined the seal on the bottom of engine at crank shaft. Do I have to disassemble engine to replace seal or is the seal replaceable externally?  

Answer
engine must come off to get to it correctly   ...  clean  crankshaft off good from seal down.   it can be pulled off and out of block  without taking engine apart.  lube crank with light oil,  and slide new seal up  in place,  and (i like to put alittle gasket sealer around mine)  before i carefully press them into  block  around crank shaft.  i use a large socket or piece of pipe to drive mine in place.