Since I already posted here I just respond here.
First correct model number for the mower is 13W
Q93AP010.
What you attempt to loosen was the neutral adjustment.
Here is where the oil fill is located.
View attachment 60930
You might, if you are good, remove that cap without removing the pulley and fan. Note these caps should be replace once removed as they do go bad with age. I have replaced several that actually had holes in them allowing water to enter the transaxle. If this happens then the unit must be removed so the oil can be changed and a new oil filter installed inside the unit.
Under the cap you will find magnet disc.
The cap pn is 187T0136300 and is about $4 plus shipping. The oil is a Synthetic 15W50 motor oil. The axle seal is PN 187T0134280 and is about $5 plus shipping. It can be change without opening up the transaxle. This is provided the local dealer don't have the parts.