1999 Mitsubishi Montero Leaking oil and smoking

This car has been very good and never had any major problem. I kept up with regular the service until about 150miles. For the last 6-8 months the car has been dripping oil and I notice drops on my driveway. Since 2-3 months ago, the car smokes especially in the morning indicating oil is getting into the exhaust system. Took it to the service shop and they told me that it may be the oil seals in the timming belt area which they replaced as well as the timming belt and water pump. That didn't stop the leak. I took it back and they now tell me it may be the cylinder head. I'm desperate because these guys seem like they will keep me going back and never resolving the problem. Unfortunately I can't afford another car right now and need to keep this one running. Someone else has suggested installing a rebuilt/used engine. I just need honest advice. Thanks.