I have just been told that my right head on my 126 chassis '85 380 SE is leaking oil.I just had a main seal replaced,after a small oil leak,It didn't leak at all for about 200 miles,then started "Gushing" a lot more than before the main seal was replaced.I took it to the local shop and they preformed a Dye test,indicating oil only seeping from the rear of the right head.
They said it needed a head gasket replaced on the right side ( they said I should do both,but the left head was rebuilt due to cam chain breakage 15k ago) the Quote from them was $1350 for the one head & $2150 to do both heads.This is just to install new head gaskets not rebuild them!
My first question is :

Is it possible for a head to leak that much oil without leaking water?
What is a good estimate to replace a head gasket on one side?
How difficult is this job?
I think I should do it myself and maybe rebuild the right head.
the car has 146k mi.
any help appreciated
thanks!!

'85 380 SE
'80 240 D
'82 300TD-girlfriends car