I recently had a Pinion Seal leak. Tried to do it my self but didn't have yoke/ gear puller so I brought it to Ford dealership and had it replaced. Now two months later I notice a small oil stain where yoke and pinion seal meet differential. It isn't even enough of a leak to drip to the ground. How long can I drive it if I keep checking oil level in differential. Will I harm any thing if I just keep oil level up to drain hole.

 

You can drive it as long as you keep level up.

But if a mechanic did the work then they should be made aware of the leak, they may want to redo it, no charge, or at least not use that kind/brand of seal again.

 

My front and rear pinion seals leak,It's been that way for 10k miles and it's been fine just check every few months.