Sorry to say, but the easiest way to replace the seal is to pull the engine. You don't have to open the engine up and can remove the old seal and replace it without disassembling any thing else. The procedure I use is as follows.
Removing an oil seal on today's small engines is not hard as long as you take your time and watch what you are doing. *Some times it can be done without removing the engine from the equipment, but I prefer to remove the engine, as it allows me to physically inspect and clean the area around the seal better. *I start by punching a hole in the metal seal ring with a scratch awl. *Next I carefully drive a blade screw driver into hole, which I use as a lever to pry out the old seal. *After removing the old seal, throughly clean the shaft with abrasive paper until it is smooth and shiny, absolutely no rust. *This will insure that you will not cut the new seal when installing. *Coat the shaft liberally with a lubricant. *I prefer assembly lube or white lithium grease. *Slowly and carefully install the new seal, which should slide on easily if you have cleaned the shaft properly. *Most seals are set about 1/16" below the edge of the seal housing. *This can be done by setting a piece of pipe, the same size as the metal portion of the seal, over the seal and slowing driving it in. *