Sorry to hi jack an old thread.
I'm experiencing this leak and stripped the cover off. One of the welch plugs has disintergrated. I thought I could just seal up and leak solved.
However, things don't always leak for no reason and on closer inspection i found traces of oil in the servo pipe - This can't be good - If I just resealed up the oil would still leak up the pipe and into the servo (That can't be good!!)
So just buy a new one as the oil is leaking because the pump is broken. £70 for peace of mind and safety.
Your desicion.
Is oil bad in the servo????