Throttle pedal pressure drops, and lose torque.

Also look for a groove worn into the engine pulley. Because of the cut angle on the MTD belts will bottom out in the groove worn into the engine pulley which will allow slippage.

I'll check for that too. I know for certain that the oil is leaking out. You can see the trail of spray as the engine is turning, and the oil level is dropping way too fast. I will replace the seal, and go from there. Let's assume there is oil residue on the belt and that was the cause of the throttle issue, how can I remove the residue from the belt? I might try dish detergent and if that doesn't work brake cleaner or engine degreaser. The last two probably aren't too great for rubber, but I think it's worth a try if the alternative is just replacing the belt anyway. What do you think?