Thanks for the detailed explanation! I did see your videos. Your girlfiend may be right, the amasol cleaned up your engine so well it made the bad seal show its ugly face. Amosol is great oil but for these older machines i have been sticking to Dino oil just because thats what was recommended. All that aside the seal was bad and was going to show up sooner or later.
Labor intensive, a little, expense not that much, machine would definately be worth the repair, it runs and sounds good. You have to pull the drive shaft the connection at the engine pulls off of a splined shaft then you can get to the seal, the wheel bearing no biggy there just pull the wheel and you can get to that. The tire rolls fairly true so i think the bearing is your problem