One of the major differences in the 60/70 type transaxle vs. the 3-4 speed versions used in the larger garden tractors, is the axle seal. The axle tubes, or extensions do not unbolt from the outside of the case. They are installed from the inside of the case. There is a bushing at the outboard end and a lip seal in the outer end of the housing. Oil must lubricate the outer bushing. The heavier duty types in the old gear drives have a sealed ball bearing in the outboard end, and an internal seal to keep the oil in the case.
When you take a good look at the manual Roger wisely suggests, the differences are easy to see. The seal in the 70 could possibly be replaced without disassembly of the transaxle. It is very difficult to do without damage to the axle where the seal rides. Not recommended, but not out of the realm of possibility.
A couple suggestions that may or may not be in the manual. If the bushings are worn, replace them. Otherwise, the leak can reappear in a short time.
Reassemble the tubes, case, and axle assemblies with out the seals. Then install the seals. Make sure all nicks, rust, and burrs are removed from the axle ends and use a thin plastic bag, masking tape or any better method of protection, to avoid damage to the seal from the sharp edges of the ring groove and key slot.
Let us know how it goes.
tommyhawk