i decided to flush the coolant system out and top up with fresh 50/50 mix,after i'd done i flipped the lid on the coolant gauge just to inspect,to my horror there was a sludgy whitey yellow goo around the top of it going down to the FULL marker,now i'm thinking its water and oil mixed,i'm also hopeing its just a goo produced off the coolant,the coolant i drained was green....

the car(96 uk turbo imprezza wagon) was bought used with 76k on the clock and has had a new radiator,i'm wondering if the radiator was replaced due to the headgasket going,but i'm thinking that if it filled up with that much oil the engine would surely be killed,theres no records of a rebuilt engine..
the coolant i drained seemed fine....

i've also noticed my revs bobbing around a little,a startup from cold usually shoots to 1500rpm then settles to 700rpm when the engine is warm
i have noticed only twice my revs hitting 1500 then down too 1000 then back up and so on before idling at 700rpm

are these the signs of a dodgy head gasket or am i just plain paranoid!!

 

The radiator may have been replaced because of a leak, so the goo could have been some old radiator leak stopper used on the old radiator, before the new one was fitted.
As for the idle hunting it sounds as if the MAF is on its way out.
Try borrowing another MAF to see if it makes a difference.
It may however be a blown head gasket.
Most garages will be able to analyse the oil / water to see if its mixing.
Hope you get it sorted
Chris