I know this will sound WRONG to many, but it does work:
Remove or disconnect battery.
Plug in electric arc welder
Do a very quick bead of weld on the countershaft.
Cool immediately with water to avoid melting the oil seal.
Repeat the above two steps until the worn bits are built up.
Use a dremel, small grinder or needle files to file new splines into the countershaft.
It's a most effective $2 repair.