Sorry if this topic has been discussed elsewhere, but a search didn't turn up anything so here goes...
My beloved '04 FX35 with 122K miles is acting like it has a leaking head gasket or worse. After what seemed like an uneventful overheating episode last summer (temp gauge went up to 3/4), dealer diagnosed a faulty thermostat... Replaced it, and flushed the cooling system, and supposedly pressure checked the system. All reported good.
Since then overflow reservoir level increases over the max line, and doesn't return coolant to the radiator when it cools down. Also notice bubbling in the reservoir after moderate drive in 70 degree weather, after engine is shut off.
Dealer reflushed the cooling system, changed radiator cap, and added UV dye to check for leaks. No leaks, hasn't overheated per the dash temp gauge, but still keeps overfilling the overflow. Seems like combustion gases might be leaking into the water jackets in one of the heads (or the block), and overpressuring it? I've been to two additional independent mechanics after Infiniti, and both seemed to think a small head gasket leak is the likely issue here. Engine seems to run just fine... Plenty of power, sounds good, and no oil use or leaks. Radiator fans working as usual, and no ECM error codes.
Anyway... I bought this car new 11 years ago, and still love it. Have babied it and done all service on time, Mobil 1 synthetic oil and filters, etc. I really would like to keep it. Any suggestions as to whether it's worth an engine rebuild or swap? Also any suggestions as to a good Nissan/Infiniti engine shop in the Chicago area? Infiniti service at my dealer here is outrageously high, and they really didn't seem interested in doing any major engine work.
Thanks for any ideas or suggestions!