Nissan Pulsar 2004: Stuck in park

I BOUGHT a 40,000km 2004 Nissan Pulsar sedan STL auto from a Nissan dealer in 2007. A few months later the automatic transmission locked in park and I was unable to drive the car. The dealer told me it would cost $880 to replace or repair the transmission and I would have to pay it because the car was out of warranty. At the time, a mechanic mentioned this had been a problem he had heard of before with this model. My local repairer referred me to an auto electrician who bypassed the system with a solenoid switch. I have been able to drive my car since then, but during the past six months the bonnet of my car has been at times extremely hot. My local mechanic found the head gasket needed to be replaced. It was decided it would be best to take it back to the Nissan dealer to be repaired, and I was quoted $1500-$2000. Can you tell me of any problems known with this model Nissan and offer any advice?