Mondeo G/box leak from selector shaft.

You are correct, it is an oil seal. I had one that leaked and took it to MSF Ford. Unfortunately they are a fast turn around part fitting service, so people working there don't need to know much about cars - and often don't in my experience. They had to take the gearbox out, then change the seal and finally put it all back together and fill up the engine. The YTS person FORGOT to put the seal in and I drove away minus £135. Later I noticed the oil all over the drive. I took it back the next day and they took it apart and advised that the clutch would need changing due to being contaminated by oil. So that was changed and I refused to pay for it as it was their mistake. I also had to wait while they ordered parts! Three days in total it took them to get it right. It's now difficult to find a decent garage with people that can diagnose a problem or take an engine to bits. Most are these fast fitting services that pressurise the workers into selling parts that are not required.

Changing the seal alone is a relatively easy job. Just prise the old one out, and tap the new one in place with a long punch.

One thing to to note though, is a new seal doesn't always cure the problem. I've seen the selector shafts wear, which causes them not to sit centrally in the seal, and they still leak.