Also worth checking that the engine breather disc is working correctly. If it is blocked, or not functioning well, the motor can create a pressure build up internally that will vent whereever it can, mag drive and genny drive being easy ways out.
Also assuming oil level is correct ? Running the motor with too much oil in sump, or primary/trans will exasparate the issue.
An old school short term fix of a little hemp string wound loosely around the drive may stop serious leaks to the wheel after a while, but you would need to make sure that it doesn't snag on the shaft. Carefully done, it can seal up the leak nicely once soaked in oil and caked in dirt and grime. More of a bodge than a cure, treating symptom not cause, but can work well. I did a similar fix on the road to a friends mag drive, which had a damaged case, using some plumbers hemp and a small piece of rag, and that was still sealing perfectly several years and several thousand miles later.
