What all is wrong with the motor?
If it is just seals why not replace them?
I have had air cooled small engines last over four thousand hours without significant work - conversely I have had ones at under two hundred hours grenade like the national debt.
Provided the motor isn't making unusual noises and passes a leak down test - just replace the seals.
I have a '98 or '99 Gravely PM 260 with over 2800 hours and the lower crank seal is leaking. The motor passes a leak down test so I just yanked the motor and clutch assembly and slapped in a new seal.
Total cost was $7.95 for the seal and the time it took me was slightly over 2 hours.
Beats the dog crap out of a $1800 motor.
Nice Try = You Suck Spelled Differently