You can download the owner manual fromhttps://lookup3.toro.com/request/request.cfm
Enter your model number like this 32-12O503 (12=hp, O=letter=Onan engine, 5=5-speed transmission, 03=numbers=parts list identifier)
Enter your serial number or use 2012345. There are other manuals there you can download but the Demystifiaction Guide is a huge electrical manual covering many years and models.
You can get the illustrated parts lists herehttp://www.partstree.com/parts/
Put Toro in the 2nd box and your 32-12O503 model number in the 3rd box.
For more info on the tractor go tohttps://lookup3.toro.com/partdex/index.cfm?xCaller=Toro
Enter your 32-12O503 model number. The transmission listed here is Peerless model 930-020. You should be able to get parts for it. Go back tohttp://www.partstree.com/parts/
Put Tecumseh in the 2nd box and 930-930-020 in the 3rd box. You can get a transmission service manual from the Files of this Yahoo Grouphttp://groups.yahoo.com/group/wheelhors ... rmanuals2/
Membership is required and the file is named "Transmission Peerless SM 1.pdf"
If you do have to replace the transmission there are many models that would fit but that is beyond my experiance. Post again in the wanted section with your location so someone close to you can respond.
Garry in Canada