seems like its leaking oil from rear of intake or rear of head gaskets,is this common on this year disco ,110k on motor

 

Sure, it will be either a valley pan gasket or the head gaskets. Are you sure you v/c gaskest bolts aren't just loose cause them to leak and go down the back of the engine?
How mechanical ar you?

 

I have my own shop,just not familiar with disco problems,gave it a quick eyeball and i cant fit a mirror behind the heads or intake from the top to see where the leak is coming from,doesnt appear to be the valve cover though

 

Then start by pullin the intake, after all, it is an old Buick engine so you shouldn't get to stuck.
Shout when you have some information and I will tell you where to go the parts needed.