Test for a head gasket leak yourself. Perform a block test. Coolant in oil = very bad. Stop driving it. It's hard to believe the dealer did give you an estimate immediately after they found oil in the coolant.
I had the exact same issue.(my spark plugs came loose) The Threads of the spark plugs in the head cracked for my Cruze so I would assume with all the other issues your car is having I would definitely suggest a head and head gasket replacementI have a 2013 Cruze 1.4L. A few weeks back the 'Service traction control' or 'service stabilitrak' lites began to intermittently show up on main dashboard, as well as sometimes the smaller 'reduced engine power lite' and 'tcs/stabiltrak lites' on the side gauge. Sometimes you'd get 1 lite, sometimes all 3, and often none. There would also be a very sporadic bucking or shaking feeling in the car, almost like a very rough idle, that was usually short duration.
Now you could go a day or 2 where it seemed to run fine, but then it would act up out of the blue. I took it to a franchise auto repair, had to bring it back twice as first time no symptoms, and they replaced spark plugs/coil pack. Some signs of oil was also noted in coolant. Ran fine a few days, then acted up again. Brought it back while acting up. It showed codes P0100,PO562,U0100. Battery and alternator had tested fine. They basically referred me to go to the dealer.
Went to dealer who said 2 of spark plugs were loose and re-torqued and also noted signs of coolant in oil. Drove fine for a few days, then once again the same problem. Brought it back to dealer who listed possible cracked head or blown head gasket as the issue and gave estimate.
Could anything else be causing this? The only other possibility I came across would be oil cooler. I just find it odd the head gasket would go on a maintained car with 90000 miles. And could the head gasket be causing stabilitrak lites to come on? Would appreciate any input.