HELP for 99 gt mustang

Hi everyone. i want to but this 99 mustang gt 35 anniveraery limited edition. i had it checked out and the guy say the motor is great. he went and checked the oil and said it wasnt no oil. He said it wasnt a good sign. He looked onder the bottom and said it was wet under there. Hesaid the oil pan gasket needed changing and the car should be fine. The owner wanted 5000 for it and said he would get it fix for me if i want the car. Do you think this is a good buy. The car has 150000 miles on it. Body is in perfect condition inside and out. I just dont want to buy a car and the motor go out. Also when you start it up it made a rattle or knocking noise. But the guy that checked the car out said it was probably bc it was low on oil. But the second time after cutting it off and starting up when he finished checking it i didnt hear that noise. I also heard a winding sound when u press gas while driving. Someone told me mustangs are rear end cars and that they make a noise you can hear from the back . Please give advice asap thank you. :wavey