I think the seal you are talking about is the powervalve cover dust seal. That seal is not designed to hold back any oil is only to prevent dirt and mud from getting to the powervalve linkage.
If you are leaking oil around it then the oil is actuallly coming from the powervalve shaft seal at the top or the actuator shaft seal where it goes into the transmission (bottom). Both of these seals can be replaced, but not without some disassembly of the associated parts.