In theory you can strip the gearbox down - you can even buy the official Peerless/Tecumseh transmission Mechanc's Handbook, which will tell you how to do it. PROBLEM 1 - Teumseh/Peerless are no longer trading! Peerless has been bought as a going concern, and will resume producion - eventually. PROBLEM 2 - internal gearbox parts (if you can find them) are RUINOUSLY expensive - of the order of £50 PER GEAR, and you will need a bucketfull if your transmission is seriously broken.
A better option is a new tranaxle - still not cheap, but a much better option, and there are some around. If you let me know the number off your's I may be able to help.
phil_saunders(a)bigfoot.com
Phil Saunders
July 2009