Small Engines (Lawn Mowers, etc.): Toro Oil Leak, toro carb

Question
I have a 1996 Toro self-propelled 6HP lawn mower. My father-in-law gave it to me and has kept it in almost brand new condition. It has not been run in several years and I have 3 questions:
- When we loaded it into the truck, it dumped a large amount of oil on the ground. It appears to be leaking from the underside of the deck where the blade is connected to the engine. I was talking to someone and they suggested the crankcase seal. This would be almost $200 to repair. Any advise on if this is possibly the problem and the degree of difficulity? I do not want to spend that kind of money on such an old mower when I can get the parts for about $20 and I have the capability and tools to do a repair like this. How would I go about repairing this? What type of oil do you recommend to refill this, being a 4 stroke motor?
-Since the mower has not been run in several years, will the carburator need to be cleaned/rebuilt? How would I go about doing this?
-The spark plug has been removed. What is the best type/most economical to replace this? Do they recommend a plug at the store?
Any help with these repairs is greatly appreciated. I am willing to do the work, but just need to know how to do it. Thank you.

Answer
The plug will depend on the engine.  With the engine make and model number, pretty much anybody who sells plugs should be able to get you the right one.

The carburetor will most likely need to come apart and be cleaned thoroughly.  I recommend either the purchase of a carburetor soak can or paying to have it cleaned.  The can runs around $40 from auto parts stores but can be re-used many times.  Spray cleaner isn't very effective for this sort of thing.  Then use a new rebuild kit when reassembling.  Again, whoever sells parts for your specific engine will have the kit.

The crank seal isn't difficult to replace on most engines.  The old one will just pry out and the new one slips back on and is tapped into place with a small hammer and block of wood.  Without a seal installer, you will need to use something to ensure the rubber lip doesn't hang up and bend the seal.  When I don't have the proper installer, I just use a small metal pick and ease the rubber lip into place while applying finger pressure to the seal.  Put a little clean oil on the inside of the seal and that will help it seal better and install easier.

Let me know if you run into any trouble.  Thanks, PK.